Transcriptome analysis reveals rice MADS13 as an important repressor of the carpel development pathway in ovules.

In angiosperms, floral homeotic genes encoding MADS-domain transcription factors regulate the development of floral organs. Specifically, members of the SEPALLATA (SEP) and AGAMOUS (AG) subfamilies form higher-order protein complexes to control floral meristem determinacy and to specify the identity of female reproductive organs. In rice, the AG subfamily gene OsMADS13 is intimately involved in the determination of ovule identity, since knock-out mutant plants develop carpel-like structures in place of ovules, resulting in female sterility. Little is known about the regulatory pathways at the base of rice gynoecium development. To investigate molecular mechanisms acting downstream of OsMADS13, we obtained transcriptomes of immature inflorescences from wild-type and Osmads13 mutant plants. Among a total of 476 differentially expressed genes (DEGs), a substantial overlap with DEGs from the SEP-family Osmads1 mutant was found, suggesting that OsMADS1 and OsMADS13 may act on a common set of target genes. Expression studies and preliminary analyses of two up-regulated genes encoding Zinc-finger transcription factors indicated that our dataset represents a valuable resource for the identification of both OsMADS13 target genes and novel players in rice ovule development. Taken together, our study suggests that OsMADS13 is an important repressor of the carpel pathway during ovule development.

Functional analysis of all AGAMOUS subfamily members in rice reveals their roles in reproductive organ identity determination and meristem determinacy.

Reproductive organ development is one of the most important steps in the life cycle of plants. Studies using core eudicot species like thale cress (Arabidopsis thaliana) and snapdragon (Antirrhinum majus) have shown that MADS domain transcription factors belonging to the AGAMOUS (AG) subfamily regulate the identity of stamens, carpels, and ovules and that they are important for floral meristem determinacy. Here, we investigate the genetic interactions between the four rice (Oryza sativa) AG subfamily members, MADS3, MADS13, MADS21, and MADS58. Our data show that, in contrast with previous reports, MADS3 and MADS58 determine stamen and carpel identity and, together with MADS13, are important for floral meristem determinacy. In the mads3 mads58 double mutant, we observed a complete loss of reproductive organ identity and massive accumulation of lodicules in the third and fourth floral whorls. MADS21 is an AGL11 lineage gene whose expression is not restricted to ovules. Instead, its expression profile is similar to those of class C genes. However, our genetic analysis shows that MADS21 has no function in stamen, carpel, or ovule identity determination.