Genetic Interaction ofOsMADS3,DROOPING LEAF, andOsMADS13in Specifying Rice Floral Organ Identities and Meristem Determinacy

Haifeng Li,Changsong Yin,Lu Zhu,Dabing Zhang,Wanqi Liang

doi:10.1104/pp.111.172080

Abstract

Grass plants develop unique floral patterns that determine grain production. However, the molecular mechanism underlying the specification of floral organ identities and meristem determinacy, including the interaction among floral homeotic genes, remains largely unknown in grasses. Here, we report the interactions of rice (Oryza sativa) floral homeotic genes, OsMADS3 (a C-class gene), OsMADS13 (a D-class gene), and DROOPING LEAF (DL), in specifying floral organ identities and floral meristem determinacy. The interaction among these genes was revealed through the analysis of double mutants. osmads13-3 osmads3-4 displayed a loss of floral meristem determinacy and generated abundant carpelloid structures containing severe defective ovules in the flower center, which were not detectable in the single mutant. In addition, in situ hybridization and yeast two-hybrid analyses revealed that OsMADS13 and OsMADS3 did not regulate each other's transcription or interact at the protein level. This indicates that OsMADS3 plays a synergistic role with OsMADS13 in both ovule development and floral meristem termination. Strikingly, osmads3-4 dl-sup6 displayed a severe loss of floral meristem determinacy and produced supernumerary whorls of lodicule-like organs at the forth whorl, suggesting that OsMADS3 and DL synergistically terminate the floral meristem. Furthermore, the defects of osmads13-3 dl-sup6 flowers appeared identical to those of dl-sup6, and the OsMADS13 expression was undetectable in dl-sup6 flowers. These observations suggest that DL and OsMADS13 may function in the same pathway specifying the identity of carpel/ovule and floral meristem. Collectively, we propose a model to illustrate the role of OsMADS3, DL, and OsMADS13 in the specification of flower organ identity and meristem determinacy in rice.

Highlights

Studies in two model eudicot plants Arabidopsis thaliana and Antirrhinum majus have suggested that MADS-box genes play critical roles in regulating flower development
Identification of new alleles of OsMADS13, OsMADS3 and DROOPING LEAF (DL) To identify rice mutants with floral defects, we screened a population of rice mutants for defective flowers in the japonica subspecies 9522 background
Previous studies in Petunia, Arabidopsis and rice revealed that the MADS-box genes belonging to the AG clade are necessary for specifying ovule identity

Summary

Introduction

Studies in two model eudicot plants Arabidopsis thaliana and Antirrhinum majus have suggested that MADS-box genes play critical roles in regulating flower development. The proposed genetic ABC model explains how three classes of genes (A, B, and C) work together in specifying floral organ identities (Coen and Meyerowitz, 1991). As one of the largest families in flowering plants, the grass family (Poaceae) contains many economically important crops such as rice (Oryza sativa), barley (Hordeum vulgare) and maize (Zea mays) (Linder and Rudall, 2005). These crops have unique floral organization and morphology which are distinct from those of eudicots and even other monocots (Grass Phylogeny Working Group, 2001; Rudall et al, 2005; Whipple et al, 2007). A rice spikelet consists of two pairs of sterile glumes (i.e. rudimentary glumes and empty glumes) and one floret that contains one lemma, one palea in whorl 1, two lodicules in whorl 2 interior to the lemma, six stamens in whorl 3 and a carpel in whorl 4 (Yuan et al, 2009;Zhang and Wilson, 2009)

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Results

Conclusion