The Arabidopsis Bsister MADSbox protein ... - Wiley Online Library

The Plant Journal (2010) 62, 203–214

doi: 10.1111/j.1365-313X.2010.04139.x

The Arabidopsis B-sister MADS-box protein, GORDITA, represses fruit growth and contributes to integument development Kalika Prasad†,‡, Xiuwen Zhang†,§, Emilio Tobo´n and Barbara A. Ambrose–,* Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand Received 27 November 2009; accepted 23 December 2009; published online 25 February 2010. * For correspondence (fax +1 718 817 8101; e-mail [email protected]). † These authors contributed equally to this work. ‡ Present address: 3584 CH, Padualaan 8, Utrecht University, The Netherlands. § Present address: University of Canberra, Kirinari St., Bruce, ACT 2617 Australia. – Present address: The New York Botanical Garden, Bronx, NY, 10458 USA.

SUMMARY The MADS-box family of transcription factors have diverse developmental roles in flower pattern formation, gametophyte cell division and fruit differentiation. The B-sister MADS-box proteins are most similar to the B-class floral homeotic proteins, and are expressed in female reproductive organs. The Arabidopsis B-sister MADS-box protein, TT16, is necessary for inner integument differentiation. We have functionally characterized the only other B-sister MADS-box gene in Arabidopsis, AGL63, renamed here as GORDITA (GOA). A loss-offunction mutation in goa or reduction of endogenous GOA expression results in larger fruits, illustrating its novel function in regulating fruit growth. Consistent with its function, GOA expression is detected in the walls of the valves and throughout the replum of the fruit. Our phenotypic and molecular analyses of 35S::GOA and goa plants show that GOA controls organ size via cell expansion. Further, functional studies of goa tt16 double mutants have shown their additive role in controlling seed coat development, and have revealed the importance of GOA expression in the outer integument. Together, our studies provide evidence of a new regulatory role for a B-sister MADS-box gene in the control of organ growth. Keywords: MADS-box B-sister gene, AGL63, plant development, fruit growth, cell expansion, integument development.

INTRODUCTION The plant MADS-box family of transcription factors play diverse developmental roles in flower pattern formation, gametophyte cell division and fruit wall differentiation (Jack, 2001; Burgeff et al., 2002; Dinneny and Yanofsky, 2005; Colombo et al., 2008). Although MADS-box proteins are present in animals, fungi and plants, there is a larger number of MADS-box proteins in the plant genomes sequenced thus far, compared with any animal or fungal genome (Alvarez-Buylla et al., 2000; Riechmann et al., 2000). The duplication and diversification of function of large multi-gene families, such as the MADS-box family, is proposed to be important for genome and morphological evolution (Purugganan et al., 1995; Moore and Purugganan, 2005). The most well-studied MADS-box proteins are the ABC floral organ identity proteins (Bowman et al., 1989; Coen and ª 2010 The Authors Journal compilation ª 2010 Blackwell Publishing Ltd

Meyerowitz, 1991). The ABC MADS-box proteins act in a combinatorial fashion to specify the four floral organs (Honma and Goto, 2001; Pelaz et al., 2001; Theissen and Saedler, 2001). Floral organ identity genes have been identified throughout the flowering plants, whereas B- and C-class genes have been found in gymnosperms (Coen and Meyerowitz, 1991; Schmidt et al., 1993; Mena et al., 1995; Kramer et al., 1998; Winter et al., 1999; Becker et al., 2000; Saedler et al., 2001). Studies of the ABC-class proteins have been used to address questions of floral organ homology, the role of duplication in morphological diversification, and have shown that the molecular basis of flower pattern formation is generally conserved throughout the angiosperms (Coen and Meyerowitz, 1991; Mena et al., 1996; Ambrose et al., 2000; Yamaguchi et al., 2006; Shan et al., 2007; Whipple et al., 2007). 203

204 Kalika Prasad et al. The MADS-box proteins closely related to the B-class floral homeotic proteins have been termed B-sister (Becker et al., 2002). It has been hypothesized that the B-class proteins are important for male reproductive organ development, whereas the B-sister proteins are important for female reproductive organ development (Becker et al., 2002). The B-sister MADS-box genes FLORAL BINDING PROTEIN 24 (FBP24) in Petunia and TRANSPARENT TESTA (TT16) in Arabidopsis have been functionally characterized, and appear to have similar developmental roles (Nesi et al., 2002; de Folter et al., 2006). TT16 is important for the proper differentiation of the inner integument (endothelium), but alone does not appear to be crucial for female reproductive development (Nesi et al., 2002). FBP24 is also necessary for proper development of the inner integument, but surprisingly is unable to complement tt16 in Arabidopsis (de Folter et al., 2006). Thus far neither TT16 nor FBP24 alone appear to be crucial for female reproductive organ development in Arabidopsis or Petunia, respectively. To further characterize the function of B-sister MADS-box proteins in Arabidopsis we characterized the B-sister gene in Arabidopsis, AGL63 (Martinez-Castilla and Alvarez-Buylla, 2003; Parenicova et al., 2003). Loss-of-function mutants for AGL63 have larger fruits, and we have renamed this gene GORDITA (GOA). Over expression of GOA results in plants that are shorter in stature, and all organs of the plant are smaller than in the wild type. GOA is expressed in ovule primordia and in ovules as the integuments arise, and its expression is later restricted to the outer integuments. GOA expression is also detected in the valves and replum of the fruit. tt16 goa plants form female reproductive structures, and this indicates that TT16 and GOA function are not essential for female reproductive development. Our functional characterization of GOA shows

that it has a role in integument development distinct from TT16 and has acquired a new role in regulating fruit growth. RESULTS The B-sister MADS-box gene, GORDITA, affects fruit growth To obtain a better understanding of the role of B-sister MADS-box genes in Arabidopsis, we characterized AGL63 mutants. We analyzed a T-DNA insertion in AGL63 (SALK_061729C) from the SALK collection (http://signal. salk.edu/cgi-bin/tdnaexpress) (Figure 1a) (Alonso et al., 2003). The most obvious defect in these T-DNA lines was the presence of larger fruits compared with the wild type (Figure 1c). Given the mutant phenotype, we renamed the gene GORDITA (GOA), which is Spanish for ‘a little bit fat’. To confirm that the fruit phenotype was caused by the T-DNA insertion in GOA, we generated a hypomorphic allele of goa (goa-2) by reducing its expression through doublestranded RNA interference (Figure 1b). The two alleles of GOA both show a similar mutant phenotype. Gross morphological analyses indicated that the goa-1 fruit was slightly wider than wild-type fruit. Seven independent lines of goa-2 were also assessed, and the fruits also appeared slightly wider than in the wild type. For a quantitative comparison, we measured stage-17 fruits of wild type, goa-1 and goa-2 (Table 1). These measurements confirmed that goa-1 fruit are significantly wider (1.26 0.14 mm versus 1.12 0.13 mm), and shorter (16.4 2.28 mm versus 17.2 1.58 mm), than wild-type fruit. We do not detect any endogenous transcripts for GOA in goa-1 inflorescences by semi-quantitative reverse transcription analysis (Figure 1d). Furthermore, double-stranded RNA interference significantly reduced the endogenous GOA transcripts in goa-2 inflorescences (Figure 1d).

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Figure 1. Phenotypic and genotypic analyses of goa. (a) Schematic map depicting the location of the T-DNA insertion in the AGL63 gene. (b) Schematic map depicting the region covered by the dsRNAiGOA construct used to make goa-2 plants. (c) Wild-type and goa-1 fruit at stage 17 (scale bar: 1 mm). (d) RT-PCR analyses of GOA mRNA in inflorescences of goa-1 (lane 1), goa-2 (lane 2) and two independent 35S::GOA lines (lanes 3 and 4) in comparison with the wild type (lane 5). Actin transcript was used as a control for cDNA levels.

ª 2010 The Authors Journal compilation ª 2010 Blackwell Publishing Ltd, The Plant Journal, (2010), 62, 203–214

GORDITA in fruit and seed development 205 Table 1 Measurements of silique length, width and seed number of stage-17 fruits of wild type, goa-1, goa-2 and 35S::GOA. Silique measurements represent means SDs. n is the number of fruits measured

Genotype

Silique width (mm)

Silique length (mm)

Seed number/fruit

Wild type goa-1 goa-2 35S:GOA

1.12 0.13 (n = 54) 1.26 0.14a (n = 52) 1.18 0.10b (n = 41) 0.76 0.10a (n = 24)

17.2 1.58 (n = 54) 16.4 2.28c (n = 52) 15.9 1.82a (n = 33) 8.87 1.17a (n = 24)

63.5 6.90 (n = 34) 58.4 11.5c (n = 37) 56.7 8.64b (n = 20) 17.7 4.10a (n = 26)

a

Significantly different from the wild type (P £ 0.0001, Student’s t-test). Significantly different from the wild type (P £ 0.01, Student’s t-test). c Significantly different from the wild type (P £ 0.05, Student’s t-test). b

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Figure 2. 35S::GOA phenotypic analyses. (a) Wild-type (left) and 35S::GOA plants at the same age (scale bar: 1 cm). (b) Close-up of 35S::GOA plants showing leaf size and shape (scale bar: 1 mm). (c) Close-up of 35S::GOA flowers (scale bar: 1 mm). Wild type (d) and 35S::GOA (e) stage-17 fruits (scale bar: 1 mm). Cleared whole-mount photos of leaf mesophyll cells of the wild type (f) and 35S::GOA (g), showing that the 35S::GOA leaf mesophyll cells are smaller than those of the wild type (scale bar: 10 lm).

Overexpression of GORDITA reduces plant size and affects fruit pattern formation To further investigate the role of GOA in growth, we generated plants in which the GOA coding region was expressed under the control of the CaMV35S promoter (35S::GOA) and then transformed into wild-type plants. Only seven independent lines survived to maturity. Three of these lines flowered but did not produce any seed. Although the surviving four gain-of-function lines all showed a similar phenotype: dwarf plants with smaller lateral organs, reduced apical dominance, reduced fecundity and delayed senescence (Figures 1d and 2). The 35S::GOA plants exhibited a dwarf phenotype with reduced apical dominance (Figure 2a). Leaves were rounder and smaller, and the stems were thinner (Figure 2a,b). The 35S::GOA inflorescences produced fewer buds. Alterations

in floral morphology were observed, including aberrantly shaped sepals, smaller petals with crinkled edges, shorter stigma and overall shorter carpels, with overextended stigmatic papillae (Figure 2c). The reduced fecundity could be the result of poor pollination as a result of shorter carpels. However, manual pollination only partially improved carpel growth and seed set. To determine if pollen viability was affected in 35S::GOA lines, mature pollen was stained by Alexander staining. 35S::GOA pollen stained similarly to wild-type pollen, indicating that pollen viability is not affected in 35S::GOA lines (data not shown). The 35S::GOA fruits were narrower, shorter, twisted and slightly indehiscent (Figure 2d,e). To further compare fruit development, we sectioned and stained wild-type and 35S::GOA stage-17B fruits. In wild-type fruit, by stage 18 the endodermal cell layer a (ena) has disintegrated and the enb layer has become completely lignified (Ferrandiz et al., 1999). In 35S::GOA


206 Kalika Prasad et al.

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Figure 3. Fruit cross sections illustrating cell number, size and morphology. The stage-17B fruits are composed of five cell layers: epidermis (Ep), mesophyll layer 1 (Ms1), mesophyll layer 2 (Ms2), mesophyll layer 3 (Ms3) and the endodermis (En). (a) Wild type, (b) goa-1, (c) goa-2 and (d) 35S::GOA (scale bars: 100 lm). The arrow in panel (d) indicates the persistence of the endodermal cell layer a (ena) cells in 35S::GOA fruits.

fruits, we observed a persistence of some ena cells and more than one layer of enb cells in portions of the fruit, suggesting that pattern formation is affected in goa fruits (Figure 3d). We also observed smaller cells throughout the fruit cell wall, and aberrant lateral vascular bundle development, in 35S::GOA compared with wild-type fruits (Figure 3d). Leaf size and shape was also affected in 35S::GOA plants. To test whether the reduced leaf length and width of 35S::GOA leaves was caused by a decrease in cell number, cell size or both, the numbers and size of the mesophyll cells in the bottom, middle and top portions of the seventh rosette leaf were measured in comparison with the corresponding portions of wild-type leaf. The number of mesophyll cells in the leaf-length direction in 35S::GOA was reduced compared with the wild type. The cell numbers along the leaf-width direction in 35S::GOA were not significantly different from the wild type. In addition, the mesophyll cell size was smaller compared with the wild type (Figure 2f,g).

GORDITA affects growth by controlling cell expansion goa fruits could be larger because of an increase in cell number or an increase in cell size or both. We made sections through stage-17B (stage according to Ferrandiz et al., 1999) fruits of wild type, goa-1, goa-2 and 35S::GOA plants, and measured cell size and cell number (Figure 3; Table 2). Arabidopsis fruit valves are composed of two endodermal layers (ena and enb), three layers of mesophyll cells and a single outer layer of epidermal cells (Figure 3a). The mesophyll layer 1 was assessed alone, whereas mesophyll layers 2 and 3 were measured together. Cell numbers of enb, mesophyll layer 1, mesophyll layers 2 and 3, and epidermal cells were counted, and no significant difference in cell number of goa-1 or goa-2 compared with the wild type was detected (Table 2). The cells in each layer were also measured. There were no significant size differences between goa and wild-type enb or epidermal cells. However, cells in

Table 2 Comparison of cell number and size in cross sections of wild type, goa-1, goa-2 and 35S::GOA carpels at stage 17B Mean cell number

Mean cell diameter (lm)

Genotype

enb

ms 1

ms 2+3

ep

enb

ms 1

ms 2+3

ep

Wild type Goa-1 goa-2 35S::GOA

195 16 (4) 200 3 (4) 187 15 (3) 191 23 (9)

74 5 (4) 81 5 (4) 66 6 (3) 71 7 (9)

202 6 (4) 213 15 (4) 185 19 (3) 163 24b (9)

106 4 (4) 116 9 (4) 107 3 (3) 103 4 (9)

7.9 2.1 (99) 7.5 2.1 (65) 8.4 2.4 (61) 5.9 2.0a (95)

29.2 9.6 (121) 33.7 11.8a (74) 35.5 12.4a (60) 26.4 12.0a (141)

23.1 7.2 (50) 27.6 5.8a (50) 26.9 6.7a (60) 20.2 6.0a (50)

26.4 8.5 (97) 28.3 9.5 (78) 28.3 7.03 (72) 22.0 8.0a (122)

Endoderm b (enb) refers to the inner sclerenchyma layer. Epidermis (ep) refers to the outer epidermal cell layer. Mesophyll 1 (ms1) refers to mesophyll cells adjacent to the sclerenchyma layer; mesophyll 2+3 (ms 2+3) cells are the mesophyll cells bounded between mesophyll 1 and the epidermal layer. Results are means SDs. Numbers in parentheses after cell numbers indicate the number of sections measured. Numbers in parentheses after cell diameters indicate the number of cells measured. a Significantly different from the wild type (P £ 0.001, Student’s t-test). bSignificantly different from the wild type (P £ 0.01, Student’s t-test). ª 2010 The Authors Journal compilation ª 2010 Blackwell Publishing Ltd, The Plant Journal, (2010), 62, 203–214

GORDITA in fruit and seed development 207

Figure 4. Quantitative RT-PCR analysis of 35S::GOA inflorescences. qRT-PCR analysis of cell proliferation or expansion genes ANGUSTIFOLIA (AN), ATHB13, CYP90D, LONGIFOLIA1 (LNG1), LONGIFOLIA2 (LNG2), ROTUNDIFOLIA3 (ROT3) and ROTUNDIFOLIA4 (ROT4) in inflorescences of 35S::GOA plants.

the goa-1 and goa-2 mesophyll layers are significantly larger than wild-type mesophyll cells (Figure 3a–c; Table 2). However, cell size and cell number differs in 35::GOA fruits compared with the wild type (Figure 3a,d; Table 2). All cell layers of 35S::GOA fruits are significantly smaller than the corresponding wild-type cell layers. Only the number of mesophyll cell layers 2 and 3 of 35S::GOA are significantly less than the number of wild-type mesophyll cell layers 2 and 3. Organ growth is controlled by cell proliferation and/or cell expansion (Mizukami, 2001; Horiguchi et al., 2006; Anastasiou and Lenhard, 2007). Organ growth is highly regulated and individual genes have been identified that control organ size and shape in Arabidopsis. We analyzed the expression of some of these growth-regulating genes in 35S::GOA inflorescences by quantitative RT-PCR (Figure 4). ROTUNDIFOLIA4 (ROT4) controls growth by inhibiting cell proliferation (Narita et al., 2004). Although ROT3, CYP90D1, LONGIFOLIA 1 and 2 (LNG1 and LNG2), ANGUSTIFOLIA (AN) and ATHB13 all affect growth by promoting cell expansion (Tsuge et al., 1996; Kim et al., 1998, 1999, 2002, 2005; Hanson et al., 2001; Lee et al., 2006). We found that the expression of AN, LNG1, LNG2 and ROT3 was reduced in 35S::GOA inflorescences compared with wild-type inflorescences (Figure 4). These results support the role of GOA as a cell expansion regulator. The loss of GOA function results in a specific change in fruit size; however, when GOA is ectopically expressed it is sufficient to repress growth throughout the plant. GORDITA is expressed in fruits, ovules and seeds Although the most obvious defect in goa was enlarged fruit, B-sister MADS-box genes are expressed in ovules and the

seed coat (Becker et al., 2002; de Folter et al., 2006). Therefore, we performed expression analyses in Arabidopsis inflorescences using RNA in situ hybridization and GUS reporter analyses. By in situ hybridization we found that GOA is expressed in sepals and developing ovules of stage-8 flowers (Figure 5a) (floral stages according to Smyth et al., 1990). In younger floral stages we detected GOA expression in the sepals; however, we did not detect GOA expression in the stamen and carpel primordia. Throughout floral development, we detect GOA expression in developing sepals and ovules (Figure 5b–d). In floral stage 12 we detected GOA expression in the connective tissue of stamens and in the carpel walls (Figure 5c). Prior to fertilization, GOA expression is detected in the sepals, ovules, carpel walls and style (Figure 5d). To better assess the expression of GOA in female reproductive organs, a 1.7-kb promoter fragment of GOA was transcriptionally fused to the GUS gene (GOA:: GUS), and then introduced into Arabidopsis wild-type plants. A total of 17 independent transgenic lines were analyzed at various stages of Arabidopsis flower development by examining reporter activity in whole-mount and histological sections. The temporal and spatial pattern of reporter activity was similar in all independent lines, although the level of GUS staining varied in some lines. In the GOA::GUS plants, the inflorescence meristem and flanking floral meristems do not exhibit GUS activity (data not shown). GUS expression is first detected in the sepals of flowers after stage 6, and is maintained throughout sepal development (Figure 5e). GUS expression was also detected in the filaments, stamen connective tissue, style, replum and carpel wall (Figure 5e–h). However, no GUS activity was observed in petals at any stage of flower development (Figure 5e). GOA::GUS plants showed dynamic reporter activity in the gynoecium throughout fruit development. GUS activity was detected in the adaxial carpel wall before fertilization, and was subsequently expressed in the adaxial carpel wall and epidermal cells as the fruit elongated and expanded (Figure 5f–i). In carpels, strong GUS expression was seen throughout the replum (Figure 5g,h). GUS expression can also be seen in the vascular bundles of the valves (Figure 5h). In developing ovules, reporter activity is detected in the nucellus of developing ovules (Figure 5i). As the integuments emerge, GUS expression is still detected in the nucellus of the developing ovule, but not in the emerging integuments (Figure 5j). After the integuments have grown to cover the nucellus, GUS staining is detected in the outer integument and embryo sac (Figure 5k). Expression is maintained in the outer integument and chalazal region of the developing seed (Figure 5l). Results of the temporal and spatial localization of GUS activity analyzed in Arabidopsis transgenic lines were similar to what was observed by RNA in situ hybridization of


208 Kalika Prasad et al.

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Figure 5. Temporal and spatial expression patterns of GOA. GOA mRNA in situ hybridization analyses on longitudinal sections (scale bars: 100 lm) (approximate floral stages according to Smyth et al., 1990). (a) GOA expression is detected in sepals (S) and developing ovules (O) of a stage-8 flower. Expression is also detected in the sepals of younger flowers; however, expression is not detected in developing stamens or carpels at these younger stages (left side of panel). (b) In stage-10 flowers, GOA expression is still detected in the sepals and developing ovules (O). (c) In stage-12 flowers, GOA expression is detected in the stamen connective tissue (SC), developing ovules and carpel endodermis (En). (d) GOA expression is seen in sepals (S), style (St), ovules (O) and the epidermis (Ep) and endodermis (En) of the carpels. (e) GOA::GUS expression is seen in developing flowers and fruit. GOA::GUS expression analyses in whole-mount (e–g, k, l; scale bars e–g, 1 mm; scale bars k and l, 100 lm) and sectioned tissue (h–j; scale bar h, 100 lm; and scale bars i and j, 10 lm). (f) Before fertilization, GOA::GUS expression is seen in the sepals (S), style (St) and stamen connective tissue (SC). (g) After fertilization, GOA::GUS expression is seen throughout the developing fruit (F). (h) GOA::GUS expression is detected in the epidermis (Ep), endodermis (En), mesophyll layer 1 (Ms) and replum (R) of the fruit, and in the outer integument (OI) of a developing seed. (i) GOA::GUS expression is detected in the endodermis (En) of developing carpels and young ovules (O), and in slightly older carpels (j) expression is still detected in the center of developing ovules (O), but not in the emerging integuments (I). (k) GOA::GUS expression is later seen in the outer integuments (OI) of nearly mature ovules. (I) GOA::GUS expression is maintained in the outer integument (OI) and chalazal (Ch) region of developing seeds.

GOA transcripts (Figure 5). We surmise that the GOA expression profile as studied by RNA localization in various stages of gynoecium development is largely recreated in the GUS activity patterns of GOA::GUS transgenic plants. These data demonstrate that controlling elements necessary for

the regulated expression of GOA during gynoecium development lie within the 1.7-kb GOA promoter region utilized in our studies. The dynamic expression pattern of GOA also suggests a likely role in female reproductive organ development.


GORDITA in fruit and seed development 209

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Figure 6. Phenotypic analyses of goa, 35S::GOA and goa tt16 seeds. Differential interference contrast (DIC) images of Hoyer’s cleared seeds at the late globular–early heart stage of embryogenesis (a–e; scale bars, 10 lm). Wild-type seed coats (a) are composed of five layers: two outer integuments (oi1 and oi2) and three inner integuments (ii1, ii1¢ and ii2). The cells of goa-1 (b) and goa-2 (c) appear longer than wild-type oi1 cells. (d) 35S::GOA ii1 and ii1¢ cells appear rounder than the wild-type cells. (e) goa tt16 oi1 cells appear longer than wild-type oi1 cells, and the ii1 and ii1¢ cells are longer and thinner than in the wild type. Safranin O alcian blue-stained seed sections at the walking stick-stage of embryogenesis (f–i; scale bar, 100 lm). There is no discernible difference between the seed coats of the wild type (f), goa-1 (g) and goa-2 (h) seeds. However, the integuments of 35S::GOA (i) appear more densely stained than those of the wild type. Seed coat color of mature dry seeds (j–o). Wild-type (j), goa-1 (k) and goa-2 (l) seeds are brown, whereas tt16 (n) and goa tt16 (o) seeds are yellow. 35S::GOA seeds are light brown (m). Tetrazolium salt assays of seed coat (p–u). Wild-type seeds (p) are impermeable to tetrazolium salts, whereas goa-1 (q), goa-2 (r), 35S::GOA (s), tt16 (t) and goa tt16 (u) seeds are permeable, as indicated by the orange color. (v–x) Epifluorescent micrographs of periodic acid Schiff’s reagent (PAS)-stained seeds (scale bars: 10 lm). Carbohydrates accumulate in the oi1 layer of the wild-type (v), goa-1 (w) and 35S::GOA (x) seeds, as indicated by the orange fluorescence. In addition, note the missing cells of the small yellow enb layer (arrowhead) and persistent ena cells (arrow) in 35S::GOA (x), compared with wild-type fruit walls (v).

GORDITA and TT16 have additive roles in seed coat development GOA is the Arabidopsis paralog of TRANSPARENT TESTA 16 (TT16), a MADS-box gene required for the proper development and pigmentation of the Arabidopsis seed coat (Nesi et al., 2002; Martinez-Castilla and Alvarez-Buylla, 2003; Parenicova et al., 2003). tt16 plants have yellow seeds, as proanthocyanidins (PAs) do not accumulate in the endothelium cells of the inner integument (Figure 6n) (Nesi et al.,

2002). However, pigmentation does accumulate in the chalazal and micropylar regions of the seed. The endothelium layer does not differentiate properly in tt16 seeds, and this is likely to be the reason that PAs do not accumulate (Nesi et al., 2002). To assess if GOA has a role in seed coat development we compared wild-type and goa seed morphology (Figure 6). goa seeds appeared similar in color to wild-type seeds (Figure 6j–l), whereas 35S::GOA seeds are light brown (Figure 6m). We performed vanillin staining and found that


210 Kalika Prasad et al. goa-1, goa-2 and wild-type seed all stained dark red, indicating that PA accumulation in the endothelial layer is not affected in goa (data not shown). These results suggest that the endothelial layer of the inner integument differentiates properly in goa seeds. The seed coat is composed of five layers: three layers compose the inner integument [ii1 (or endothelial layer), ii1¢ and ii2], and two layers compose the outer integument (oi1 and oi2) (Figure 6a). To assess seed coat development, we cleared wild-type, goa-1, goa-2 and 35S::GOA whole seeds using Hoyer’s medium, and stained cross-sections of all genotypes using safranin O and alcian blue. All five integument layers are formed in goa-1, goa-2 and 35S::GOA developing seeds (Figure 6b–d). However, in goa seeds the cells of the outer integument layer (oi1) are long and narrow compared with the more square-shaped oi1 cells of the wild type (Figure 6a–c). Whereas the cells of the oi1 layer are square-shaped in 35S::GOA developing seeds, the inner integument cells (ii1 and ii1¢) appear larger and more round than the inner integument cells of the wild type (Figure 6a,d). Safranin O alcian blue-stained sections of more mature seeds show no discernible difference in the integument layers of goa and wild-type seeds (Figure 6f–h); however, the integument layers of 35S::GOA seeds appear more densely stained (Figure 6i). In addition, goa and 35S::GOA seeds appeared slightly longer than wild-type seeds; however, no difference in seed weight from that of the wild type was detected (data not shown). We performed tetrazolium salt assays to further assess seed coat differences between the wild type and goa (Figure 6p–s). Seed coats that are permeable to tetrazolium salts are reduced to a formazan orange-red dye (Debeaujon et al., 2000). Wild-type seeds are not permeable to tetrazolium salts (Figure 6p), whereas goa and 35S::GOA seeds are permeable (Figure 6q–s), which suggests that there are structural defects in the seed coats of goa mutants. Starch grains accumulate in the oi1 layer of developing seeds (Windsor et al., 2000). To determine if starch grain accumulation is affected in goa mutants, we stained seed sections with periodic acid Schiff’s reagent (PAS). Carbohydrates fluoresce orange with PAS-stained sections under epifluorescence. It appears that starch accumulates normally in the oi1 layer of goa-1 and 35S::GOA compared with the wild type (Figure 6v–x). It appears that GOA plays a role in the development of the seed coat, and its role is likely to be specific to the outer seed coat, which would be consistent with its expression pattern in developing seeds. To assess any redundancy between GOA and TT16 in development, we constructed goa-1 tt16-1 double mutant plants. goa-1 tt16-1 plants produce viable seeds, indicating that both proteins are dispensable for proper ovule development. goa-1 tt16-1 seeds are yellow in color, similar to tt16 single mutants (Figure 6j,n,o). Not surprisingly, goa1 tt16-1 seeds are permeable to tetrazolium salts, as are the

single mutants (Figure 6q,t,u). goa-1 tt16-1 seed coats are composed of five integument layers; however, the developing oi1 cells appear similar to goa oi cells, and goa-1 tt16-1 inner integument ii1 cells appear similar to tt16 ii1 cells (Figure 6a–c,e). Therefore, the role of GOA and TT16 in seed coat development appears additive. DISCUSSION Arabidopsis B-sister MADS-box genes The divergence between the B and B-sister proteins has been dated to approximately 550 Mya (Nam et al., 2003). The B-sister group of MADS-box proteins has been identified in flowering plants and gymnosperms: ZMM17 from Zea mays, DEFH21 from Antirrhinum majus, ABS/TT16 from Arabidopsis thaliana, FBP24 from Petunia hybrida, AeAP3-2 from Asarum europaeum and GGM13 from Gnetum gnemon (Becker et al., 2000, 2002; Kramer and Irish, 2000; Nesi et al., 2002). B-sister MADS-box genes are expressed in the ovule and envelope in gymnosperms, and in the ovule and integuments of angiosperms, supporting the hypothesis that the gymnosperm envelope is homologous with the angiosperm integument (Becker et al., 2000). The temporal and spatial expression pattern for TT16 is not known; however, we found GOA to be expressed in ovules, outer integuments, sepals, stamens, style, replum and carpel walls (Figure 5). Therefore the Arabidopsis B-sister MADSbox gene, GOA, has an expression domain that overlaps with other B-sister MADS-box genes. It has been hypothesized that B-sister MADS-box genes are important for female reproductive organ (ovule) development (Becker et al., 2000). However, functional analyses of FBP24 in Petunia and TT16 in Arabidopsis did not uncover a role for either of these genes in ovule development (de Folter et al., 2006). Although GOA is expressed in early stages of ovule development, our functional characterization of GOA did not reveal a role for GOA alone in ovule development. We assessed whether there is some redundancy in TT16 and GOA function in ovule specification; however, the tt16 goa plants formed fully functional ovules. Therefore, Arabidopsis B-sister MADS-box genes alone do not appear to be important for ovule development. It is possible that TT16 and GOA do have a role in ovule development, but that other MADS-box proteins mask this role. Yeast three-hybrid studies showed that FBP24 interacted with C- and E-class proteins or with D- and E-class proteins, suggesting that these higher order complexes may be important for female organ development (de Folter et al., 2006; Tonaco et al., 2006). GORDITA is important for proper outer integument development Although GOA and TT16 are not functionally redundant in ovule development, both GOA and TT16 have roles in seed


GORDITA in fruit and seed development 211 coat development (Figure 6). TT16 is required for the proper differentiation of one of the three inner integument layers: the endothelium. Our expression and functional analyses did not show a role for GOA in the development of any inner integument layers. However, in goa the outer integument layer (oi1) is aberrantly shaped during early stages of development, which suggests that GOA is necessary for at least the early development of the outer integument (Figure 6b,c). It is possible that GOA only affects the size of the cells in the outer integument, also showing a role for growth in the seed. However, tetrazolium salt assays show that goa mutants are permeable to these salts, which indicates that there are structural differences in the goa seed coat (Figure 6p–s) (Debeaujon et al., 2000; Lepiniec et al., 2006). In the wild type, starch granules are deposited in the outer integuments, and these contribute to wall thickening as the seed coat develops (Windsor et al., 2000). However, we found that starch granules accumulated in the outer integuments of goa mutants in a similar way to wild type (Figure 6v–x). In 35S::GOA plants the oi1 develops as in the wild type; however, the inner integument (ii1) cells are rounder and appear more cytoplasmically dense, and resemble the outer integument morphology (Figure 6a,d). These morphological analyses suggest that GOA plays a role in outer integument differentiation. The seed coat of 35S::GOA seeds are light brown compared with the wild-type brown seeds (Figure 6j,m). Two different flavonoids accumulate in Arabidopsis seeds (Lepiniec et al., 2006). PAs accumulate in the ii1 layer and flavonols accumulate in the oi1 layer. tt16 seeds are yellow, as PAs do not accumulate in the ii1 layer. As goa appears to specifically affect the oi1 layer, further analyses are needed to measure flavonol accumulation in goa and 35S::GOA seeds. In goa tt16 plants, the developing ii1 and oi1 layers do not differentiate as in the wild type, indicating that GOA and TT16 have diverged in function for seed coat development. GORDITA is a new regulator of growth Remarkably, determinate organs grow to the same size when compared within a species, yet the size of these organs compared across closely related species can vary immensely. The control of organ growth is highly regulated, and individual genes have been identified that control organ size and shape. The final size of an organ depends on two phases of growth: cell proliferation, followed by cell expansion (Horiguchi et al., 2006; Anastasiou and Lenhard, 2007). During cell proliferation, cells increase in size and then divide. Only after cell proliferation is complete does cell expansion occur. The most obvious defect in goa plants is larger fruits. Our analyses show a new role for a B-sister MADS-box gene in specifically repressing fruit growth. We characterized goa mutants and found that the increase in fruit size resulted from an increase in cell size and not cell number (Figure 3 and Table 2). These results show that GOA

regulates fruit growth by repressing cell expansion of the mesophyll cells of the fruit wall. 35S::GOA plants were dwarfed, and all lateral organs were smaller (Figure 2). Expression analyses by qRT-PCR in inflorescences show that the expression of the polar cell expansion genes LNG1, LNG2, AN and ROT3 are all reduced in 35S::GOA, compared with the wild type (Figure 4). These expression results corroborate our phenotypic analyses that GOA affects size mainly through cell size. We also assessed the expression of these genes in goa inflorescences, and found a slight increase in the expression of LNG1 and LNG2 (Figure S1). This increased expression is likely to be an indirect effect of the expanded cells found in goa fruits. Further analyses are needed to determine the direct downstream targets of GOA in fruit growth. Although we have uncovered a new role for GOA in fruit growth it is also possible that TT16 has a role in growth, as the published 35S::TT16 phenotype resembles 35S::GOA plants (Nesi et al., 2002). In addition, goa, 35S::GOA and tt16 seeds all appeared different in size compared with wild-type seeds. Further analyses of seed size are needed to assess the role of GOA and TT16 in seed growth and shape. Organ shape and size in animals and plants is regulated by mechanisms that measure the overall size of the organ, and not of the individual cells (Day and Lawrence, 2000; Anastasiou and Lenhard, 2007). It has been suggested that organs can measure their size independently in two dimensions – length and width – and that a dimension-sensing mechanism is based on morphogen gradients (Day and Lawrence, 2000; Horiguchi et al., 2006; Tsukaya, 2008). In animals, morphogen gradients originate from compartment borders (Day and Lawrence, 2000). In plants, this morphogen gradient could be set up by hormones or by proteins like KLU (Anastasiou and Lenhard, 2007; Anastasiou et al., 2007). It has also been suggested that growth is controlled by an extrinsic mechanism, a morphogen gradient, and an intrinsic mechanism, pattern formation (Day and Lawrence, 2000). In 35S::GOA fruits, the ena and enb layers of the fruit were not normally patterned, suggesting that GOA might interact with proteins involved in fruit patterning. In Arabidopsis, much is known about the two separate developmental processes of fruit pattern formation and organ growth regulation. However, little is known about the coordination of growth and pattern formation that must occur during organogenesis. Molecular genetic analyses between the fruit growth gene GOA and known pattern formation genes will allow us to investigate the coordination of organogenesis. EXPERIMENTAL PROCEDURES Plant materials The goa-1 mutant (SALK_061729C) was found by screening the SIGnAL database (http://signal.salk.edu/cgi-bin/tdnaexpress;


212 Kalika Prasad et al. Alonso et al., 2003). The goa-2 mutant was generated by doublestranded RNA interference as described in following section. The tt16-1 mutant (N57500) was obtained from the Nottingham Arabidopsis Stock Centre (NASC, http://arabidopsis.info). goa-1 and tt16-1 were backcrossed to the Columbia ecotype three times before beginning morphological studies and making the goa-1 tt16-1 double mutants. All plants were grown at 22C under constant light.

with a Zeiss (http://www.zeiss.com) Axiophot Microscope equipped with Nomarsky optics (differential interference contrast, DIC), and digital images were captured using AXIOVISION 3.0 (Zeiss). Composite figures were made with Adobe Creative Suite (http:// www.adobe.com).

Plasmid construction and plant transformation

The measurements of fruit width and length were performed as previously described (Lease et al., 2001). Briefly, the fifth to 10th siliques from the primary inflorescence of between eight and 10 plants per genotype were used to measure the length and width of stage-17 siliques. For measurement of seed number, seeds were counted under a dissecting microscope from fruits at early stage 18, which were then soaked in 1:1 ethanol:acetic acid overnight and moved to 1 N NaOH. Student’s t-tests (http://www.physics. csbsju.edu/stats/) were used for the statistical analyses. Silique cell number and size were quantified from stained cross sections as previously described, except stage-17B fruits were used (VivianSmith and Koltunow, 1999).

All PCR amplifications for plasmid construction were performed with a combination of Taq and Pwo polymerases (Roche, http:// www.roche-applied-science.com). All constructs were sequenced to verify the integrity of the sequences. The GOA cDNA was amplified by PCR using 63FCDNA (5¢-GCAACCACATTTCTTTCTC-3¢) and 63RcDNA (5¢-GTATTTGGGCCTGGTTGTGG-3¢), and then cloned into P-GEM T-easy (Promega, http://www.promega.com). To construct the 35S::GOA plants, the GOA full-length cDNA was cloned into the EcoRI site between the constitutive CaMV 35S promoter and the nopaline synthase (nos) terminator sequences of vector pART7. The entire cassette comprising the 35S promoter-GOA cDNA-nos terminator, was excised out by NotI and cloned into binary vector pART27. To generate knock-down lines by double-stranded RNA interference, the GOA cDNA fragment comprising the I, K-box and C-terminus regions was used. The GOA cDNA was cloned into the KpnI site of pHANNIBAL (CSIRO, http://www.csiro.au) in antisense orientation. The IKC region of GOA was amplified using 003AGL63Bam5 (5¢-CGGGATCCCGATTTCTGCTCCAAC-3¢) and 004AGL63Xba3 (5¢-GCTCTAGAGGGCCTGGTTGTGG-3¢), and then cloned into the BamHI and XbaI sites of the pHANNIBAL vector already containing the cDNA in the antisense orientation of GOA. The entire cassette comprising 35S promoter-dsRNAiGOA-nos terminator was excised by NotI and cloned into binary vector pART27. The GOA::GUS construct was generated by amplifying the 1.7-kb GOA promoter (from )1 to )1721 bp using 001AGL63 (5¢-GCATGAGCTGAGACGCAATC-3¢) and 002AGL63 (5¢-CCTTTCCTCATCTTCCAATCG-3¢), and then cloned into pGEM T-easy (Promega). BamHI sites were added by PCR and the BamHI fragment was cloned into the plant binary vector pCAMBIA1381Xc (CSIRO), such that translation initiates with the GOA start codon, followed by a linker contributing 17 codons, and then the uidA (GUS) gene beginning at its second codon. These recombinant binary vectors were introduced into Agrobacterium tumefaciens. Arabidopsis transformation was performed as previously described (Clough and Bent, 1998).

Plant genotyping Genotyping of goa-1 was performed using 63FcDNA, 007AGL63 (5¢-ACATGCTCGAGCTCGCAAG-3¢) and the SALK LBb1 primer (5¢-GCGTGGACCGCTTGCTGCAACT-3¢). Genotyping of tt16-1 was performed using primers TT16-ATG (5¢-CATGGGTAGAGGGAAGATAG-3¢), TT16-6R (5¢-CGGTCAATGAGTTGAGGCATCCA-3¢) and LBBAR1 (5¢-CAACCCTCAACTGGAAACGGGCCGGA-3¢).

Histological analyses and microscopy Safranin O and alcian blue staining of tissue sections was performed as previously described (Roeder et al., 2003). Tissue sections were stained with PAS as previously described (Pearse, 1953). To view the seed coat layers, Hoyer’s clearing was performed as previously described (Nesi et al., 2002). Anatomical analyses of leaf mesophyll cells were performed as previously described (Narita et al., 2004). Tetrazolium salt assays were performed as previously described (Debeaujon et al., 2000). Whole-mount photos were taken with a Nikon (http://www.nikoninstruments.com) stereomicroscope equipped with a Nikon DSLR camera. Sectioned tissue was viewed

Fruit and seed measurements

In situ hybridizations RNA in situ hybridization for GOA transcripts was performed with gene-specific RNA probes. The GOA IKC fragment utilized in RNA interference (see Plasmid construction and plant transformation) was subcloned into pBlueScript (KS). DIG-labeled probes for detection of GOA were prepared as described in Ambrose et al. (2000). BamH1 linearized pBlueScript (KS)-GOA was transcribed with T7 RNA polymerase to make an antisense probe, whereas the XbaI linearized plasmid was used to generate a sense probe synthesis with T3 RNA polymerase. Hybridizations were performed as in Ambrose et al. (2000).

GUS assay Arabidopsis inflorescences were processed as previously described (Sessions et al., 1999), except 2.5 mM potassium ferricyanide and 2.5 mM potassium ferrocyanide were used in the staining solution.

Expression analyses by PCR Semi-quantitative RT-PCR on total RNA from wild-type or 35S::GORDITA, goa-1 and goa-2 was performed. To determine the expression levels of GORDITA in these genetic backgrounds total RNA was isolated from inflorescences using Spectrum TM plant total RNA kit (Sigma-Aldrich, http://www.sigmaaldrich.com). A 2-lg portion of total RNA was used for reverse transcription using gene-specific primers. A 2-ll volume of the cDNA was used for each PCR reaction. For semi-quantitative RT-PCR analysis, cDNA was amplified for 30 PCR cycles using AGL63FP and AGL63RP primers. For real-time quantitative RT-PCR analysis, first-strand cDNA was synthesized from 1 lg of total RNA and M-MuLV RT (Fermentas, http://www.fermentas.com) enzyme. Two biological replicates for each genetic background (wild type or 35S::GOA) were subjected to three technical replicates for quantitative PCR (qPCR) reactions using the ABI Prism 7000 system (http://www.appliedbiosystems. com). The difference in threshold cycle (Ct) value between 35S::GORDITA and the wild type for the normalized transcript levels was used to calculate fold regulation of the differentially regulated genes. The primers used in the study are listed in Table S1.

ACKNOWLEDGEMENTS Funding for this research was provided by Massey University. Thanks to Tynisha Smalls for excellent technical assistance. BAA is


GORDITA in fruit and seed development 213 grateful for support from Lewis B. and Dorothy Cullman and NYBG for the completion of this work.

SUPPORTING INFORMATION Additional Supporting Information may be found in the online version of this article: TAIR annotation spreadsheet. Figure S1. Quantitative RT-PCR analyses of goa inflorescences. Table S1. Primers used in this study. Please note: As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer-reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.

REFERENCES Alonso, J.M., Stepanova, A.N., Leisse, T.J. et al. (2003) Genome-wide insertional mutagenesis of Arabidopsis thaliana. Science, 301, 653–657. Alvarez-Buylla, E.R., Pelaz, S., Liljegren, S.J., Gold, S.E., Burgeff, C., Ditta, G.S., Ribas de Pouplana, L., Martinez-Castilla, L. and Yanofsky, M.F. (2000) An ancestral MADS-box gene duplication occurred before the divergence of plants and animals. Proc. Natl Acad. Sci. USA, 97, 5328–5333. Ambrose, B.A., Lerner, D.R., Ciceri, P., Padilla, C.M., Yanofsky, M.F. and Schmidt, R.J. (2000) Molecular and genetic analyses of the silky1 gene reveal conservation in floral organ specification between eudicots and monocots. Mol. Cell, 5, 569–579. Anastasiou, E. and Lenhard, M. (2007) Growing up to one’s standard. Curr. Opin. Plant Biol. 10, 63–69. Anastasiou, E., Kenz, S., Gerstung, M., MacLean, D., Timmer, J., Fleck, C. and Lenhard, M. (2007) Control of plant organ size by KLUH/CYP78A5-dependent intercellular signaling. Dev. Cell, 13, 843–856. Becker, A., Winter, K.U., Meyer, B., Saedler, H. and Theissen, G. (2000) MADSBox gene diversity in seed plants 300 million years ago. Mol. Biol. Evol. 17, 1425–1434. Becker, A., Kaufmann, K., Freialdenhoven, A., Vincent, C., Li, M.A., Saedler, H. and Theissen, G. (2002) A novel MADS-box gene subfamily with a sistergroup relationship to class B floral homeotic genes. Mol. Genet. Genomics, 266, 942–950. Bowman, J.L., Smyth, D.R. and Meyerowitz, E.M. (1989) Genes directing flower development in Arabidopsis. Plant Cell, 1, 37–52. Burgeff, C., Liljegren, S.J., Tapia-Lopez, R., Yanofsky, M.F. and AlvarezBuylla, E.R. (2002) MADS-box gene expression in lateral primordia, meristems and differentiated tissues of Arabidopsis thaliana roots. Planta, 214, 365–372. Clough, S.J. and Bent, A.F. (1998) Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana. Plant J. 16, 735–743. Coen, E.S. and Meyerowitz, E.M. (1991) The war of the whorls: genetic interactions controlling flower development. Nature, 353, 31–37. Colombo, M., Masiero, S., Vanzulli, S., Lardelli, P, .Kater, M.M. and Colombo, L. (2008) AGL23, a type I MADS-box gene that controls female gametophyte and embryo development in Arabidopsis. Plant J. 54, 1037–1048. Day, S.J. and Lawrence, P.A. (2000) Measuring dimensions: the regulation of size and shape. Development, 127, 2977–2987. Debeaujon, I., Leon-Kloosterziel, K.M. and Koornneef, M. (2000) Influence of the testa on seed dormancy, germination, and longevity in Arabidopsis. Plant Physiol. 122, 403–414. Dinneny, J.R. and Yanofsky, M.F. (2005) Drawing lines and borders: how the dehiscent fruit of Arabidopsis is patterned. Bioessays, 27, 42–49. Ferrandiz, C., Pelaz, S. and Yanofsky, M.F. (1999) Control of carpel and fruit development in Arabidopsis. Annu. Rev. Biochem. 68, 321–354. de Folter, S., Shchennikova, A.V., Franken, J., Busscher, M., Baskar, R., Grossniklaus, U., Angenent, G.C. and Immink, R.G. (2006) A Bsister MADSbox gene involved in ovule and seed development in petunia and Arabidopsis. Plant J. 47, 934–946. Hanson, J., Johannesson, H. and Engstrom, P. (2001) Sugar-dependent alterations in cotyledon and leaf development in transgenic plants expressing the HDZhdip gene ATHB13. Plant Mol. Biol. 45, 247–262.

Honma, T. and Goto, K. (2001) Complexes of MADS-box proteins are sufficient to convert leaves into floral organs. Nature, 409, 525–529. Horiguchi, G., Ferjani, A., Fujikura, U. and Tsukaya, H. (2006) Coordination of cell proliferation and cell expansion in the control of leaf size in Arabidopsis thaliana. J. Plant. Res. 119, 37–42. Jack, T. (2001) Plant development going MADS. Plant Mol. Biol. 46, 515–520. Kim, G.T., Tsukaya, H. and Uchimiya, H. (1998) The ROTUNDIFOLIA3 gene of Arabidopsis thaliana encodes a new member of the cytochrome P-450 family that is required for the regulated polar elongation of leaf cells. Genes Dev. 12, 2381–2391. Kim, G.T., Tsukaya, H., Saito, Y. and Uchimiya, H. (1999) Changes in the shapes of leaves and flowers upon overexpression of cytochrome P450 in Arabidopsis. Proc. Natl. Acad. Sci. USA, 96, 9433–9437. Kim, G.T., Shoda, K., Tsuge, T., Cho, K.H., Uchimiya, H., Yokoyama, R., Nishitani, K. and Tsukaya, H. (2002) The ANGUSTIFOLIA gene of Arabidopsis, a plant CtBP gene, regulates leaf-cell expansion, the arrangement of cortical microtubules in leaf cells and expression of a gene involved in cellwall formation. EMBO J. 21, 1267–1279. Kim, G.T., Fujioka, S., Kozuka, T., Tax, F.E., Takatsuto, S., Yoshida, S. and Tsukaya, H. (2005) CYP90C1 and CYP90D1 are involved in different steps in the brassinosteroid biosynthesis pathway in Arabidopsis thaliana. Plant J. 41, 710–721. Kramer, E.M. and Irish, V.F. (2000) Evolution of the petal and stamen developmental programs: evidence from comparative studies of the lower eudicots and basal angiosperms. Int. J. Plant Sci. 161, S29–S40. Kramer, E.M., Dorit, R.L. and Irish, V.F. (1998) Molecular evolution of genes controlling petal and stamen development: duplication and divergence within the APETALA3 and PISTILLATA MADS-box gene lineages. Genetics, 149, 765–783. Lease, K.A., Wen, J., Li, J., Doke, J.T., Liscum, E. and Walker, J.C. (2001) A mutant Arabidopsis heterotrimeric G-protein beta subunit affects leaf, flower, and fruit development. Plant Cell, 13, 2631–2641. Lee, Y.K., Kim, G.T., Kim, I.J., Park, J., Kwak, S.S., Choi, G. and Chung, W.I. (2006) LONGIFOLIA1 and LONGIFOLIA2, two homologous genes, regulate longitudinal cell elongation in Arabidopsis. Development, 133, 4305–4314. Lepiniec, L., Debeaujon, I., Routaboul, J.M., Baudry, A., Pourcel, L., Nesi, N. and Caboche, M. (2006) Genetics and biochemistry of seed flavonoids. Annu. Rev. Plant. Biol. 57, 405–430. Martinez-Castilla, L.P. and Alvarez-Buylla, E.R. (2003) Adaptive evolution in the Arabidopsis MADS-box gene family inferred from its complete resolved phylogeny. Proc. Natl Acad. Sci. USA, 100, 13407–13412. Mena, M., Mandel, M.A., Lerner, D.R., Yanofsky, M.F. and Schmidt, R.J. (1995) A characterization of the MADS-box gene family in maize. Plant J. 8, 845– 854. Mena, M., Ambrose, B.A., Meeley, R.B., Briggs, S.P., Yanofsky, M.F. and Schmidt, R.J. (1996) Diversification of C-function activity in maize flower development. Science, 274, 1537–1540. Mizukami, Y. (2001) A matter of size: developmental control of organ size in plants. Curr. Opin. Plant Biol. 4, 533–539. Moore, R.C. and Purugganan, M.D. (2005) The evolutionary dynamics of plant duplicate genes. Curr. Opin. Plant Biol. 8, 122–128. Nam, J., de Pamphilis, C.W., Ma, H. and Nei, M. (2003) Antiquity and evolution of the MADS-box gene family controlling flower development in plants. Mol. Biol. Evol. 20, 1435–1447. Narita, N.N., Moore, S., Horiguchi, G., Kubo, M., Demura, T., Fukuda, H., Goodrich, J. and Tsukaya, H. (2004) Overexpression of a novel small peptide ROTUNDIFOLIA4 decreases cell proliferation and alters leaf shape in Arabidopsis thaliana. Plant J. 38, 699–713. Nesi, N., Debeaujon, I., Jond, C., Stewart, A.J., Jenkins, G.I., Caboche, M. and Lepiniec, L. (2002) The TRANSPARENT TESTA16 locus encodes the ARABIDOPSIS BSISTER MADS domain protein and is required for proper development and pigmentation of the seed coat. Plant Cell, 14, 2463– 2479. Parenicova, L., de Folter, S., Kieffer, M. et al. (2003) Molecular and phylogenetic analyses of the complete MADS-box transcription factor family in Arabidopsis: new openings to the MADS world. Plant Cell, 15, 1538– 1551. Pearse, A.G.E. (1953) Histochemistry,theoretical and applied. Boston: Little Brown. Pelaz, S., Tapia-Lopez, R., Alvarez-Buylla, E.R. and Yanofsky, M.F. (2001) Conversion of leaves into petals in Arabidopsis. Curr. Biol. 11, 182–184.


214 Kalika Prasad et al. Purugganan, M.D., Rounsley, S.D., Schmidt, R.J. and Yanofsky, M.F. (1995) Molecular evolution of flower development: diversification of the plant MADS-box regulatory gene family. Genetics, 140, 345–356. Riechmann, J.L., Heard, J., Martin, G. et al. (2000) Arabidopsis transcription factors: genome-wide comparative analysis among eukaryotes. Science, 290, 2105–2110. Roeder, A.H., Ferrandiz, C. and Yanofsky, M.F. (2003) The role of the REPLUMLESS homeodomain protein in patterning the Arabidopsis fruit. Curr. Biol. 13, 1630–1635. Saedler, H., Becker, A., Winter, K.U., Kirchner, C. and Theissen, G. (2001) MADS-box genes are involved in floral development and evolution. Acta Biochim. Pol. 48, 351–358. Schmidt, R.J., Veit, B., Mandel, M.A., Mena, M., Hake, S. and Yanofsky, M.F. (1993) Identification and molecular characterization of ZAG1, the maize homolog of the Arabidopsis floral homeotic gene AGAMOUS. Plant Cell, 5, 729–737. Sessions, A., Weigel, D. and Yanofsky, M.F. (1999) The Arabidopsis thaliana MERISTEM LAYER 1 promoter specifies epidermal expression in meristems and young primordia. Plant J. 20, 259–263. Shan, H., Zhang, N., Liu, C., Xu, G., Zhang, J., Chen, Z. and Kong, H. (2007) Patterns of gene duplication and functional diversification during the evolution of the AP1/SQUA subfamily of plant MADS-box genes. Mol. Phylogenet. Evol. 44, 26–41. Smyth, D.R., Bowman, J.L. and Meyerowitz, E.M. (1990) Early flower development in Arabidopsis. Plant Cell 2, 755–767.

Theissen, G. and Saedler, H. (2001) Plant biology. Floral quartets. Nature, 409, 469–471. Tonaco, I.A., Borst, J.W., de Vries, S.C., Angenent, G.C. and Immink, R.G. (2006) In vivo imaging of MADS-box transcription factor interactions. J. Exp. Bot. 57, 33–42. Tsuge, T., Tsukaya, H. and Uchimiya, H. (1996) Two independent and polarized processes of cell elongation regulate leaf blade expansion in Arabidopsis thaliana (L.) Heynh. Development, 122, 1589–1600. Tsukaya, H. (2008) Controlling size in multicellular organs: focus on the leaf. PLoS Biol. 6, e174. Vivian-Smith, A. and Koltunow, A.M. (1999) Genetic analysis of growth-regulator-induced parthenocarpy in Arabidopsis. Plant Physiol. 121, 437–451. Whipple, C.J., Zanis, M.J., Kellogg, E.A. and Schmidt, R.J. (2007) Conservation of B class gene expression in the second whorl of a basal grass and outgroups links the origin of lodicules and petals. Proc. Natl. Acad. Sci. USA, 104, 1081–1086. Windsor, J.B., Symonds, V.V., Mendenhall, J. and Lloyd, A.M. (2000) Arabidopsis seed coat development: morphological differentiation of the outer integument. Plant J. 22, 483–493. Winter, K.U., Becker, A., Munster, T., Kim, J.T., Saedler, H. and Theissen, G. (1999) MADS-box genes reveal that gnetophytes are more closely related to conifers than to flowering plants. Proc. Natl Acad. Sci. USA, 96, 7342–7347. Yamaguchi, T., Lee, D.Y., Miyao, A., Hirochika, H., An, G. and Hirano, H.Y. (2006) Functional diversification of the two C-class MADS box genes OSMADS3 and OSMADS58 in Oryza sativa. Plant Cell, 18, 15–28.
