Molecular Cloning and Characterization of Three Glucosinolate Transporter (GTR) Genes from Chinese Kale

Chinese kale is a native vegetable in Southern China and the flowering stalk is the most commonly used edible part due to its high glucosinolate content and other nutritional qualities. The GTR protein played important roles in the glucosinolate transport process. In this study, three BocGTR1 genes were cloned from Chinese kale for the first time. Their gene structure, physicochemical properties, signal peptides, transmembrane structures, functional domains, second and third-order protein structures, and phylogenetic relationships were predicted. The expression levels of BocGTR1a and BocGTR1c were much higher than those of BocGTR1b in various tissues, especially in leaves and buds. In addition, the expression patterns of three genes were examined under various abiotic stresses or hormone treatment, including those induced by wounding, heat stress, methyl jasmonate, salicylic acid, salt, and MgCl₂ treatment. BocGTR1a and BocGTR1c were strongly induced by wounding and heat stress. The expression of BocGTR1a and BocGTR1c was significantly silenced in plants transformed by RNAi technology. Total glucosinolate content was significantly decreased in mature leaves and increased in roots of RNAi-transformed plants compared to wild-type plants. In addition, we found that BocGTR1a and BocGTR1c may participate in glucosinolate accumulation in different tissues with a selection for specific glucosinolates. These results indicated that BocGTR1a and BocGTR1c may be the key genes involved in the glucosinolate accumulation in different tissues of Chinese kale.