Figure 9.

A Proposed Model for RLA1 in Rice BR Signaling.

(A) In wild-type plants, low BR level leads to the phosphorylation of both RLA1 and OsBZR1 by GSK2. The phosphorylated RLA1 is targeted for degradation by an unknown mechanism, and BR-responsive gene expression is blocked (left). With high BR levels, GSK2 activity is inhibited, leading to the accumulation of unphosphorylated RLA1, which activates OsBZR1 transcriptional activity to regulate BR-responsive gene expression (right).

(B) In rla1 plants, because of the lack of RLA1, OsBZR1 cannot activate or inhibit the BR-responsive gene expression with (right) or without (left) BRs.