Characterization of maize sex-determination gene orthologs in rice (Oryza sativa L. japonica cv. Nipponbare)

Ensuring food security will be a crucial problem in the coming decades. Heterosis, the phenomenon where hybrid progeny exhibit increased vigor in comparison to their inbred parents, has been exploited to increase agricultural yield in maize (Zea mays) for decades due to its monoecious reproductive state. Unisexuality in maize is genetically controlled due to the concerted action of the Tassel seed1 (ts1), Tassel seed2 (ts2), and Silkless1 (sk1) genes. Orthologs of the Tassel seed genes and sk1 can be found in the rice genome even though rice maintains an ancestral cosexual floral state. This study identified maize sex determination (SD) orthologs in rice, and included subsequent characterization of these orthologs in wild-type and transgenic rice tissues. Rice ts1 (rTs1) was confirmed to be japonica rice MSU-TIGR gene locus LOC_Os04g37430, rice ts2 (rTs2) was confirmed to be locus LOC_Os03g18740, and rice sk1 ( rSk1) was confirmed to be LOC_Os04g44354 based on bioinformatic analysis. RT-PCR and multiplexed Taqman qRT-PCR experiments showed that these genes were broadly expressed throughout the plant during vegetative growth in leaves, shoots, and roots, and the rTs1 and rTs2 genes are expressed in inflorescences. Transgenic analysis, using GUS reporter translational fusions, revealed that rTs1 and rTs2 are expressed in leaf vasculature and that rTs2 is expressed in spikelet vasculature, developing anthers, and emerging roots. These results suggest that SD orthologs in rice may be involved in development, specifically with programmed cell death processes, which may involve jasmonic acid signaling