PHENOTYPIC ALTERATIONS OF PETAL AND SEPAL BY ECTOPIC EXPRESSION OF A RICE MADS BOX GENE IN TOBACCO

Floral organ development is controlled by a group of regulatory factor s containing the MADS domain. In this study, we have isolated and char acterized a cDNA clone from rice, OsMADS3, which encodes a MADS-domain containing protein. The OsMADS3 amino acid sequence shows over 60% id entity to AG of Arabidopsis, PLE of Antirrhinum majus, and AG/PLE homo logues of petunia, tobacco, tomato, Brassica napus, and maize. Homolog y in the MADS box region is most conserved. RNA blot analysis indicate d that the rice MADS gene was preferentially expressed in reproductive organs, especially in stamen and carpel. In situ localization studies showed that the transcript was present primarily in stamen and carpel . The function of the rice OsMADS3 was elucidated by ectopic expressio n of the gene under the control of the CaMV 35S promoter in a heterolo gous tobacco plant system. Transgenic plants exhibited an altered morp hology and coloration of the perianth organs. Sepals were pale green a nd elongated. Limbs of the corolla were split into sections which in s ome plants became antheroid structures attached to tubes that resemble d filaments. The phenotypes mimic the results of ectopic expression of dicot AG gene or AG homologues. These results indicate that the OsMAD S3 gene is possibly an AG homologue and that the AG genes appear to be structurally and functionally conserved between dicot and monocot.