A possible working mechanism for rice SVP-group MADS-box proteins as negative regulators of brassinosteroid responses.

Most SVP-group MADS-box genes control meristem identity and flowering time. In rice, their roles in regulating the former are well-conserved; however, their involvement in determining the latter is not significant. Characteristically, rice SVP-group MADS-box proteins work as negative regulators in brassinosteroid (BR) responses. To elucidate the molecular mechanism, we studied the localization patterns for these proteins and found that, unexpectedly, they were not specific in the nucleus, whether expressed alone or simultaneously. Interestingly however, OsMADS22 and OsMADS47 were translocated into the nucleus along with OsMADS50 while OsMADS55 inhibited the nuclear localization of OsMADS50. An overlapping cis-element exists between the CArG motif and ARF binding site on the promoter region of OsBLE, which is upregulated by BR treatment and in SVP RNAi plants. These observations suggest that BR-mediated signals may induce target gene expression by removing the SVP-group MADS-box proteins that preoccupy the promoters of BR downstream genes.