Functional conservation and diversification between rice OsMADS22/OsMADS55 and Arabidopsis SVP proteins.

MADS-box transcription factors play pivotal roles in several aspects of plant growth and development. The Arabidopsis SHORT VEGETATIVE PHASE (SVP) protein mediates the integration of signals involved in the control of flowering time and flower development by interacting with MADS-box proteins. In the rice genome, three SVP-like genes (OsMADS22, OsMADS47, and OsMADS55) are present. To investigate the functional conservation of these SVP-like genes in rice and Arabidopsis, the phenotypes of transgenic Arabidopsis plants overexpressing OsMADS22 and OsMADS55 were analyzed. Overexpression of OsMADS22 and OsMADS55 led to abnormal floral morphologies including leaf-like sepals, whereas only OsMADS55 expression caused delayed flowering via downregulation of FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1). Yeast two-hybrid assays revealed that OsMADS22 and OsMADS55 interacted with Arabidopsis AGL24 and AP1, but only OsMADS55 interacted with FLC. Overexpression of OsMADS55, but not OsMADS22, complemented the early flowering phenotype and ambient temperature-insensitive flowering phenotype seen in svp mutants, suggesting that OsMADS55 regulates flowering time associated with ambient temperature responses in Arabidopsis. Taken together, our data are consistent with functional conservation and diversification between Arabidopsis and rice SVP-like genes involved in controlling flowering time and flower development.