About this Research Topic
Glutathione transferases (GSTs) constitute an ancient superfamily of multifunctional and diverse enzymes. GSTs modify a broad range of molecules including secondary metabolites and exogenous substrates, which are often referred to as xenobiotics, for their detoxification. They can be categorized into evolutionary distinct, multiple subunit classes with a mixture of highly specific or overlapping functions.
GSTs were originally considered to serve mainly for xenobiotic detoxification until discovery of their involvement in numerous endogenous functions. For example, GSTs having a serine (or tyrosine) as a catalytic residue catalyze a wide range of reactions involving the conjugation of glutathione (GSH; γ-Glu–Cys–Gly) to electrophilic compounds to form more soluble peptide derivatives for further export and storage. They also display GSH-dependent peroxidase and isomerase activities. On the contrary, GSTs exhibiting a cysteine as catalytic residue catalyze the opposite reaction (deglutathionylation) and exhibit thiol-transferase or reductase activities. Besides these catalytic functions, GSTs can also bind non-substrate ligands (ligandin properties) and function in intracellular transport.
An increasing body of work has implicated their role in an array of different functions, including biotic and abiotic stress tolerance, biosynthesis, binding and transport of secondary metabolites as well as the maintenance of the reduced state of the cellular antioxidant pool. Plant GSTs also participate in the regulation of cell signaling and plant growth and development. Several GSTs contribute in hormone metabolism or action and are induced by auxin, ethylene, abscisic acid, jasmonic acid and salicylic acid. GSTs conjugate GSH to oxylipins such as 12-oxophytodienoic acid (OPDA) and phytoprostanes, thereby reducing their reactivity.
All plants possess a large number of GST isoenzymes which can be grouped into three super families: (i) cytosolic (or soluble) GSTs, (ii) mitochondrial and peroxisomal GSTs, and (iii) microsomal GSTs. To date, only a small number of these proteins have been functionally characterized. There are several new findings on the identification, classification and regulation of plant GST gene families, and progress was made in recent years in the fields of genomics, proteomics, protein crystallography, diversity and substrate specificity of GSTs. However, there are still several unresolved questions regarding their mechanism of action, interactions with other proteins, and their influence on plant development and stress-responsive signaling.
This Research Topic aims to gather current knowledge about the plant GSTome. Submission of different types of articles - Reviews, Mini-Reviews, Methods, and Original Research Articles - is welcome to give an overview of this diverse enzyme family. The focus will be on, but not limited to, the following aspects:
• Studies on molecular evolution and classification
• Structural specificities, catalytic and ligand-binding properties
• Functions in endogenous metabolism and xenobiotic detoxification processes
• Interaction of GSTs with GSH, GSH-synthesizing and GSH-requiring enzymes, and other endogenous compounds (e.g. antioxidants, secondary metabolites, oxylipins)
• Modulation of cellular redox status, redox control, defense signaling
• Roles in hormone metabolism, homeostasis, or mechanism of action in plant development
• Roles in tolerance against biotic and abiotic stresses, interactions with other organisms
• Biotechnological application of GSTs in plant improvement or environmental quality
In spite of many recent research discoveries in the plant GST field, many aspects of their roles and functions in plant metabolism, detoxification, subcellular location, genomic structure, and regulation of GST expression remain to be determined. As a result, the overarching goal of our Research Topic is to present the most up-to-date findings regarding plant GST function and establish a framework for publishing new advances in this exciting field of plant biology.
Keywords: Glutathione Transferases, Detoxification, Glutathionylation, Ligand Binding, Redox State
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