Overexpression of the glucosyltransferase gene BoaUGT74B1 enhances the accumulation of indole glucosinolates in Chinese kale

Abstract

Glucosinolates are a diverse class of secondary metabolites that play a vital role in the plant defense response. Here, we investigated the function of the UDP-glucosyltransferase 74B1 (UGT74B1) gene in glucosinolate biosynthesis in Chinese kale. A 1401 bp coding sequence of BoaUGT74B1 was cloned from Chinese kale cultivar ‘Sijicutiao’. Among different organs, BoaUGT74B1 has the highest expression level in young seeds. Among different flower tissues, BoaUGT74B1 has the highest expression level in the pistil; the gene was downregulated in flower tissues as flowers matured. Subcellular localization showed that BoaUGT74B1 is located in chloroplasts. A purified ~50 kD fusion protein was obtained from Escherichia coli after prokaryotic expression of BoaUGT74B1. BoaUGT74B1 introduced into the white-flower cultivar ‘Sijicutiao’ and yellow-flower cultivar ‘Fuzhouhuanghua’ of Chinese kale by Agrobacterium-mediated transformation was strongly in both cultivars. Expression levels of BoaUGT74B1 in the overexpressed plants ‘Sijicutiao’ and ‘Fuzhouhuanghua’ were 1.53- to 2.93-fold and 3.07- to 5.30-fold higher, respectively than that of the wild type; the total indole glucosinolate content in these two overexpressed plants was 1.30- to 7.11-fold and 2.13- to 4.44-fold higher, respectively, compared with that in wild-type plants. Each indole glucosinolate accumulated in significant amounts in all overexpressed plants; 4‑methoxy glucobrassicin enhanced most in ‘Sijicutiao’ overexpressed plants, in concentrations up to 12.14-fold higher than the control; glucobrassicin enhanced most in ‘Fuzhouhuanghua’ overexpressed plants, reaching levels 22.76x that of its wild-type counterpart. Therefore, these findings indicate that BoaUGT74B1 plays an important role in the accumulation of indole glucosinolates in Chinese kale, and suggest the possible usefulness of this gene to improve the nutritional quality and resistance against biotic stress of Chinese kale.