OsPRA2 fine-tunes rice brassinosteroid receptor.

Brassinosteroids (BRs) are a kind of plant hormones that regulate many important agronomic traits. Although the framework of the BR signaling pathway has been outlined, detailed working mechanisms at several steps of this pathway, especially at the BR receptor level, need to be further elucidated. Recently we have reported that a rice small G protein, OsPRA2, bound to the BR receptor OsBRI1 at the plasma membrane (PM) and inhibited its kinase activity and its interaction with the co-receptor OsBAK1, leading to a lower sensitivity to BR treatment and dephosphorylation of OsBZR1. In this follow-up study, we identified an OsPRA2-interacting protein through yeast 2 hybrid system, which is annotated as a C2-domain containing GTPase activating protein (OsGAP1). Overexpression of OsGAP1 in Arabidopsis resulted in a phenotype mimic to BR-deficiency, implying that the GTPase activity of OsPRA2 is also involved in regulating BR signaling. In addition, we observed that, besides colocalizing at the PM, OsPRA2 was also colocalized with OsBRI1 in small granules near PM, suggesting that the function of OsPRA2 in vesicle traffic may contribute to the regulation of OsBRI1.