OsMADS32 is a monocot specific MIKC^c type MADS-box gene that plays an important role in regulating rice floral meristem and organs identity, a crucial process for reproductive success and rice yield. However, its underlying mechanism of action remains to be clari fied. Here, we characterized a hypomorphic mutant allele of OsMADS32/CFO1, cfo1-3 and identi fied its function in controlling rice flower development by bioinformatics and protein-protein interaction analysis. The cfo1-3 mutant produces defective flowers,including loss of lodicule identity, formation of ectopic lodicule or hull-like organs and decreased stamen number,mimicking phenotypes related to the mutation of B class genes. Molecular characterization indicated that mis-splicing of OsMADS32 transcripts in the cfo1-3 mutant resulted in an extra eight amino acids in the K-domain of OsMADS32 protein.By yeast two hybrid and bimolecular fluorescence complementation assays, we revealed that the insertion of eight amino acids or deletion of the internal region in the K1 subdomain of Os MADS32 affects the interaction between OsMADS32 with PISTILLATA(PI)-like proteins OsMADS2 and OsMADS4. This work provides new insight into the mechanism by which Os MADS32 regulates rice lodicule and stamen identity, by interaction with two PI-like proteins via its K domain.
Anther cuticle and pollen exine act as protective envelopes for the male gametophyte or pollen grain, but the mechanism underlying the synthesis of these lipidic polymers remains unclear. Previously, a tapetum‐expressed CYP703A3, a putative cytochrome P450 fatty acid hydroxylase, was shown to be essential for male fertility in rice(Oryza sativa L.). However,the biochemical and biological roles of CYP703A3 has not been characterized. Here, we observed that cyp703a3‐2 caused by one base insertion in CYP703A3 displays defective pollen exine and anther epicuticular layer, which differs from Arabidopsis cyp703a2 in which only defective pollen exine occurs. Consistently, chemical composition assay showed that levels of cutin monomers and wax components were dramatically reduced in cyp703a3‐2 anthers. Unlike the wide range of substrates of Arabidopsis CYP703A2, CYP703A3 functions as an in‐chain hydroxylase only for a specific substrate, lauric acid, preferably generating 7‐hydroxylated lauric acid. Moreover, chromatin immunoprecipitation and expression analyses revealed that the expression of CYP703A3 is directly regulated by Tapetum Degeneration Retardation, a known regulator of tapetum PCD and pollen exine formation. Collectively, our results suggest that CYP703A3 represents a conserved and diversified biochemical pathway for in‐chain hydroxylation of lauric acid required for the development of male organ in higher plants.
