Identification of DELLA Genes and Key Stage for GA Sensitivity in Bolting and Flowering of Flowering Chinese Cabbage

Abstract

Flowering Chinese cabbage (<i>Brassica campestris</i> L. ssp. <i>chinensis</i> var. <i>utilis</i> Tsen et Lee) is an important and extensively cultivated vegetable in south China, and its stalk development is mainly regulated by gibberellin (GA). DELLA proteins negatively regulate GA signal transduction and may play an important role in determining bolting and flowering. Nevertheless, no systematic study of the <i>DELLA</i> gene family has been undertaken in flowering Chinese cabbage. In the present study, we found that the two-true-leaf spraying of gibberellin A3 (GA₃) did not promote bolting but did promote flowering, whereas the three-true-leaf spraying of GA₃ promoted both bolting and flowering. In addition, we identified five <i>DELLA</i> genes in flowering Chinese cabbage. All five proteins contained DELLA, VHYNP, VHIID, and SAW conserved domains. Protein-protein interaction results showed that in the presence of GA₃, all five DELLA proteins interacted with BcGID1b (GA-INSENSITIVE DWARF 1b) but not with BcGID1a (GA-INSENSITIVE DWARF 1a) or BcGID1c (GA-INSENSITIVE DWARF 1c). Their expression analysis showed that the <i>DELLA</i> genes exhibited tissue-specific expression, and their reversible expression profiles responded to exogenous GA₃ depending on the treatment stage. We also found that the <i>DELLA</i> genes showed distinct expression patterns in the two varieties of flowering Chinese cabbage. <i>BcRGL1</i> may play a major role in the early bud differentiation process of different varieties, affecting bolting and flowering. Taken together, these results provide a theoretical basis for further dissecting the DELLA regulatory mechanism in the bolting and flowering of flowering Chinese cabbage.