ISOLATION AND CHARACTERIZATION OF A RICE MADS BOX GENE BELONGING TO THE AGL2 GENE FAMILY

The MADS box genes that encode regulatory proteins play important sole s in both the formation of newer meristem and the determination of flo ral organ identity. We have, characterized a flower-specific cDNA that belongs to the AGL2 gene family from rice, designated OsMADS5. The cD NA displays the structure of a typical plant MADS box gene, which cons ists of a MADS domain, It domain, a short I region between the MADS an d K domain, and the C-terminal region downstream of the K domain. The gene was classified as a member of the AGL2 gene family from sequence homology analysis. The OsMADS5 protein is the most similar to OsMADS1 of rice (72% identity). Dr spatial and temporal RNA blot analyses, the OsMADS5 gene was expressed preferentially in anthers and weakly in ca rpels. During newer development, the gene was more highly expressed in the early floral stage than in the late. To study the functions of th e gene, the cDNA clone was expressed ectopically using the CaMV 35S pr omoter in a heterologous tobacco plant system. Transgenic plants of Os MADS5 exhibited the phenotype of weak dwarfism and early flowering. Th ese results indicate that OsMADS5 is structurally related to the AGL2 family and may be involved in controlling flowering time.