Genome-wide characterization of BraABCB transporters reveals their potential roles in hormone responses in Brassica rapa var. parachinensis.

Abstract

Key message: Thirty-six BraABCB genes were identified in Brassica rapa var. parachinensis; expression and interaction analyses suggest BraABCB27 and BraABCB28 as hormone-responsive candidates associated with BRI1-related proteins. ABCB transporters are ATP-dependent membrane proteins that mediate the transport of diverse substrates, including phytohormones, and play important roles in plant development and environmental adaptation. Previous studies in Arabidopsis have shown that several ABCB proteins participate in phytohormone transport, including auxin and brassinosteroid transport, whereas the functions of their homologs in Brassica rapa var. parachinensis remain poorly understood. In this study, 36 BraABCB genes were identified and classified into four phylogenetic groups. Conserved domain analysis showed that BraABCB proteins contain typical nucleotide-binding domains and transmembrane domains. Chromosomal distribution, collinearity, and Ka/Ks analyses suggested that the BraABCB family is evolutionarily conserved and mainly subject to purifying constraints. Promoter analysis and RT-qPCR assays of selected Group IV BraABCB genes revealed diverse expression patterns and responses to drought, high temperature, brassinolide, and indole-3-acetic acid treatments. Subcellular localization assays showed that selected Group IV BraABCB proteins exhibited predominant plasma membrane localization. Notably, BraABCB27 and BraABCB28, two close AtABCB1/AtABCB19-related homologs, showed detectable physical associations with BRI1-related proteins in BiFC and split-ubiquitin yeast two-hybrid assays. Together, these results provide a genome-wide characterization of the BraABCB gene family and identify BraABCB27 and BraABCB28 as candidate genes for future studies of their possible associations with BR-related membrane processes and hormone-regulated growth responses in B. rapa var. parachinensis.