Brp SPL 9 ( B rassica rapa ssp. pekinensis SPL 9 ) controls the earliness of heading time in C hinese cabbage

Summary The leafy heads of cabbage ( B rassica oleracea ), C hinese cabbage ( B rassica rapa ssp. pekinensis ), Brussels sprouts ( B . oleracea ssp. gemmifera ) and lettuce ( L actuca sativa ) comprise extremely incurved leaves that are edible vegetable products. The heading time is important for high quality and yield of these crops. Here, we report that B rpSPL9‐2 ( B. rapa ssp. pekinensis SQUAMOSA PROMOTER BINDING‐LIKE 9‐2 ), a target gene of micro RNA brp‐miR156, controls the heading time of C hinese cabbage. Quantitative measurements of leaf shapes, sizes, colour and curvature indicated that heading is a late adult phase of vegetative growth. During the vegetative period, miR156 levels gradually decreased from the seedling stage to the heading one, whereas BrpSPL9‐2 and BrpSPL15‐1 m RNA s increased progressively and reached the highest levels at the heading stage. Overexpression of a mutated miR156‐resistant form of BrpSPL9‐2 caused the significant earliness of heading, concurrent with shortening of the seedling and rosette stages. By contrast, overexpression of miR156 delayed the folding time, concomitant with prolongation of the seedling and rosette stages. Morphological analysis reveals that the significant earliness of heading in the transgenic plants overexpressing BrpSPL9‐2 gene was produced because the juvenile phase was absent and the early adult phase shortened, whereas the significant delay of folding in the transgenic plants overexpressing Brp‐MIR156a was due to prolongation of the juvenile and early adult phases. Thus, miR156 and BrpSPL9 genes are potentially important for genetic improvement of earliness of C hinese cabbage and other crops.