Genome-wide analysis of SUMO conjugation pathway members in broccoli and the involvement of BoSIZ1 in response to ABA

The small ubiquitin-like protein modifier (SUMO) is a conserved protein that modifies target proteins by attaching to them, changing their functions, localizations, and interactions. However, there is limited knowledge regarding the process of SUMOylation in broccoli (Brassica oleracea var. italica), a highly nutritious vegetable that is widely consumed. In this study, a total of 40 genes including 6 families associated with the SUMOylation pathway were identified in the broccoli genome. Western blot analysis using AtSUMO1 antibody showed that SUMOylation levels increased as broccoli sprouts grew, peaking at 11 days when true leaves were fully developed. RT-qPCR analysis of 10 SUMO pathway genes showed that most of them were upregulated in response to high temperature, NaCl, and abscisic acid (ABA) stimuli within 24 h. Western blot analysis showed changes in SUMOylation dynamics in broccoli sprouts under abiotic stress conditions, regulating SUMOylated proteins. The nuclear localization of the SUMO E3 ligase BoSIZ1a was determined, along with its SUMOylation activity in vivo. Overexpression of BoSIZ1a in Arabidopsis resulted in reduced sensitivity to ABA and decreased expression of ABA-responsive genes (AtABF3, AtADH, AtEm6, AtABI5, AtRAB18, and AtRD29A). Collectively, this study reveals the organization of the broccoli SUMOylation system and highlights the crucial function of SUMOylation in broccoli's response to abiotic stress, as well as the significant contribution of BoSIZ1a in the plant's ABA response.