Biochemical functions of the glutathione transferase supergene family of Larix kaempferi

Glutathione transferases (GSTs), which are ubiquitous in plants, play a major role in the detoxification of xenobiotics and oxidative stress metabolism. Due to their role in herbicide detoxification, previous studies of plant GSTs have mainly focused on agricultural plants. In contrast, functional information regarding gymnosperm GSTs is scarce. In this study, we cloned 27 full-length GST genes from the deciduous conifer Larix kaempferi, which is widely distributed across the cooler regions of the northern hemisphere. As with the angiosperm GST gene family, Larix GSTs are divided into eight classes, and tau class GSTs are the most numerous. Compared to the other seven classes of GSTs, Larix tau GST genes show substantially more variation in their expression patterns. The purified Larix GST proteins showed different substrate specificities, substrate activities, and kinetic characteristics. The pH and temperature profiles of purified Larix GST proteins showed broad optimum pH and temperature ranges for enzymatic activity, suggesting that Larix GSTs have evolutionary adaptations to various adverse environments. Taken together, this study provides comprehensive insight into the gymnosperm GST gene family.