Plant glutathione S-transferases, a tale of theta and tau

Glutathione S-transferases (GSTs, EC 2.5.1.18) are ubiquitous enzymes that catalyze the addition of glutathione to a wide variety of substrates. Plant GSTs have been studied mainly in relation to their role in the detoxification of herbicides, mostly in maize. Recently, several gst genes have been isolated as genes that respond to the plant hormone auxin with increased transcription. Pathogen infections and other treatments have also been found to lead to increased expression of gst genes. It is now apparent that different types of plant gst genes and activities exist in most plant species, but their functional relationships and their relationships to the action of auxin are still poorly understood. Here, a historic overview on plant GSTs will be presented. Based on primary sequence differences, a new class of plant GSTs, tau, will be proposed. The possible roles of auxin and oxidative stress in inducing gst genes will be discussed. Hopefully this review will help develop new ideas and stimulate new research to study the functions of the ever growing family of plant GSTs.