Abstract

Floral organ identity is defined by organ homoetic genes whose coordinated expression is crucial for the time and place of floral organ formation. Here, we report molecular cloning and characterization of the rice STAMENLESS 1 (SL1) gene involved in floral development. The sl1 mutant largely resembles the rice B class gene mutant spw1, both exhibit homeotic conversions of lodicules and stamens to palea/lemma-like organs and carpels. Additionally, sl1 produces flowers with varied numbers of inner floral organs, and amorphous tissues without any floral organ identities were frequently formed in whorl 3 and 4. We also show that SL1 specifies lodicule and stamen identities through positive transcriptional regulation of SPW1/OsMADS16 expression. SL1 encodes a member of zinc finger protein of C2H2 type, closely related to JAG of Arabidopsis. The functional divergence between SL1 and JAG implies that SL1 was co-opted for its distinctive roles in specification of floral organ identity in rice after the lineage split from Arabidopsis.