A Critical Role of OsMADS1 in the Development of the Body of the Palea in Rice

OsMADS1 plays crucial roles in the specification of floral organ identity and the determinacy of floral meristem in rice (Oryza sativa). Here we isolated a rice mutant cy15 with defective spikelets. Map-based cloning identified cy15 as a novel mutation in the C terminus of OsMADS1. Severe cy15 spikelets contained normal inner whorl organs but defective paleas, opposite to four abnormal whorls of Osmads1 flowers reported previously. In the cy15 spikelets, the size of the body was remarkably reduced in paleas, indicating a critical role of OsMADS1 in its differentiation. Moreover, the development of palea was impaired in the early stage of the cy15 spikelets. The sub-subcellular location of the mutant OsMADS1 was also affected in cy15. On the other hand, the truncated C terminus of the mutant OsMADS1 from cy15 still showed a significant transcriptional activator function. Meanwhile, though the mutant OsMADS1 retained intact M, I and K domains, its interactions with two highly homologous A-class proteins, OsMADS15 or OsMADS14, were weakened or abolished. Our data suggested that the C-terminal sequence of OsMADS1 might be required for maintaining normal morphology of spikelets in rice.