A 2-oxoglutarate-dependent dioxygenase, GLUCORAPHASATIN SYNTHASE 1 (GRS1) is a major determinant for different aliphatic glucosinolates between radish and Chinese cabbage.

Abstract

Glucosinolates (GSLs) are secondary metabolites in Brassicaceae plants and play a defensive role against a variety of abiotic and biotic stresses. Also, it exhibits anti-cancer activity against cancer cell in human. Different profiles of aliphatic GSL compounds between radish and Chinese cabbage were previously reported. However, molecular details underlying the divergent profile between two species were not clearly understood. In this study, we found that major difference of aliphatic GSLs profiles between two species is determined by the dominantly expressed genes in first step of the secondary modification phase, which are responsible for enzymatic catalysis of methylthioalkyl-glucosinolate. For instance, active expression of GLUCORAPHASATIN SYNTHASE 1 (GRS1) gene in radish play an important role in the production of glucoraphasatin (GRH) and glucoraphenin (GRE), a major aliphatic GSLs in radish. Meanwhile, Chinese cabbage was found to merely produce glucoraphasatin (GRH), instead producing glucoraphanin (GRA) and gluconapin (GNP) due to the mere expression of GRS1 homologs and abundant expressions of FLAVIN-CONTAINING MONOOXYGENASES (FMO GS-OX) homologs in Chinese cabbage. In addition, we noticed that wounding treatment on leaf tissues substantially enhanced the production of aliphatic and benzenic GSLs in both Chinese cabbage and radish, indicating that GSLs are wound-induced defensive compounds in both Chinese cabbage and radish plants.