BcSOC1 Promotes Bolting and Stem Elongation in Flowering Chinese Cabbage

Flowering Chinese cabbage is one of the most economically important stalk vegetables. However, the molecular mechanisms underlying bolting, which is directly related to stalk quality and yield, in this species remain unknown. Previously, we examined five key stem development stages in flowering Chinese cabbage. Here, we identified a gene, BcSOC1 (SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1), in flowering Chinese cabbage using transcriptome analysis, whose expression was positively correlated with bolting. Exogenous gibberellin (GA3) and low-temperature treatments significantly upregulated BcSOC1 and promoted early bolting and flowering. Additionally, BcSOC1 overexpression accelerated early flowering and stem elongation in both Arabidopsis and flowering Chinese cabbage, whereas its knockdown dramatically delayed bolting and flowering and inhibited stem elongation in the latter; the inhibition of stem elongation was more notable than delayed flowering. BcSOC1 overexpression also induced cell expansion by upregulating genes encoding cell wall structural proteins, such as BcEXPA11 (cell wall structural proteins and enzymes) and BcXTH3 (xyloglucan endotransglycosidase/hydrolase), upon exogenous GA3 and low-temperature treatments. Moreover, the length of pith cells was correlated with stem height, and BcSOC1 interacted with BcAGL6 (AGAMOUS-LIKE 6) and BcAGL24 (AGAMOUS-LIKE 24). Thus, BcSOC1 plays a vital role in bolting and stem elongation of flowering Chinese cabbage and may play a novel role in regulating stalk development, apart from the conserved function of Arabidopsis SOC1 in flowering alone.