OCTOPUS regulates BIN2 to control leaf curvature in Chinese cabbage.

Abstract

Heading is one of the most important agronomic traits for Chinese cabbage crops. During the heading stage, leaf axial growth is an essential process. In the past, most genes predicted to be involved in the heading process have been based on leaf development studies in <i>Arabidopsis</i>. No genes that control leaf axial growth have been mapped and cloned via forward genetics in Chinese cabbage. In this study, we characterize the inward curling mutant <i>ic1</i> in <i>Brassica rapa</i> ssp. <i>pekinensis</i> and identify a mutation in the <i>OCTOPUS</i> (<i>BrOPS</i>) gene by map-based cloning. OPS is involved in phloem differentiation in <i>Arabidopsis</i>, a functionalization of regulating leaf curvature that is differentiated in Chinese cabbage. In the presence of brassinosteroid (BR) at the early heading stage in <i>ic1</i>, the mutation of BrOPS fails to sequester brassinosteroid insensitive 2 (BrBIN2) from the nucleus, allowing BrBIN2 to phosphorylate and inactivate BrBES1, which in turn relieves the repression of <i>BrAS1</i> and results in leaf inward curving. Taken together, the results of our findings indicate that BrOPS positively regulates BR signaling by antagonizing BrBIN2 to promote leaf epinastic growth at the early heading stage in Chinese cabbage.