Organisation and structural evolution of the rice glutathione S-transferase gene family

Abstract

Glutathione S-transferases (GSTs) comprise a large family of key defence enzymes against xenobiotic toxicity. Here we describe the comprehensive characterisation of this important multigene family in the model monocot species rice [ Oryza sativa(L.)]. Furthermore, we investigate the molecular evolution of the family based on the analysis of (1) the patterns of within-genome duplication, and (2) the phylogenetic relationships and evolutionary divergence among rice, Arabidopsis, maize and soybean GSTs. By in-silico screening of the EST and genome divisions of the Genbank/EMBL/DDBJ database we have isolated 59 putative genes and two pseudogenes, making this the largest plant GST family characterised to date. Of these, 38 (62%) are represented by genomic and EST sequences and 23 (38%) are known only from their genomic sequences. A preliminary survey of EST collections shows a large degree of variability in gene expression between different tissues and environmental conditions, with a small number of genes (13) accounting for 80% of all ESTs. Rice GSTs are organised in four main phylogenetic classes, with 91% of all rice genes belonging to the two plant-specific classes Tau (40 genes) and Phi (16 genes). Pairwise identity scores range between 17 and 98% for proteins of the same class, and 7 and 21% for interclass comparisons. Rapid evolution by gene duplication is suggested by the discovery of two large clusters of 7 and 23 closely related genes on chromosomes 1 and 10, respectively. A comparison of the complete GST families in two monocot and two dicot species suggests a monophyletic origin for all Theta and Zeta GSTs, and no more than three common ancestors for all Phi and Tau genes.

Binding and Glutathione Conjugation of Porphyrinogens by Plant Glutathione Transferases

“…Subsequent studies with mammalian GSTs showed that this "ligandin" activity was shown with both tetrapyrroles and porphyrins (4,5), with similar activities demonstrated with GSTs from oat plants (6,7). As is the case in animals, GSTs are also encoded by a superfamily of genes in plants such as Arabidopsis (8) and rice (9) and can be grouped into the tau, phi, theta, zeta, lambda, and dehydroascorbate reductase classes (9,10). As part of a long term program, we are engaged in functionally characterizing these proteins in crops, where they have important roles in conjugating herbicides and other agrochemicals with GSH (11).…”

“…Specific classes of GSTs, like the dehydroascorbate reductases and zeta enzymes, have been ascribed roles in ascorbate recycling and tyrosine catabolism, respectively (10,12). However, the natural functions of the large and plant-specific phi (GSTF) and tau (GSTU) proteins, which dominate the superfamily in Arabidopsis and rice (9), are almost entirely unknown.…”

Extensive Functional Diversification of thePopulusGlutathioneS-Transferase Supergene Family

“…To identify GST genes in Populus trichocarpa, TBLASTN searches of the P. trichocarpa genome database were performed using 53 full-length GST protein sequences of Arabidopsis thaliana (Dixon et al, 2002), 61 of rice (Oryza sativa; Soranzo et al, 2004), and 575 of other plants, animals, fungi, and bacteria (see Supplemental Data Set 1 online). These 689 fulllength GSTs represent 35 classes defined by the NCBI conserved domain database (Marchler-Bauer et al, 2005).…”

Cytosolic Action of Phytochelatin Synthase

“…The conjugation of electrophilic molecules to GSH is catalyzed by the action of glutathione S-transferases (GSTs). In plants, GSTs are encoded by a large gene family with approximately 50 members in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa; Soranzo et al, 2004;Edwards and Dixon, 2005), highlighting the importance of GS conjugate formation for the metabolism of endogenous compounds and the detoxification of noxious compounds such as herbicides. GS conjugates are predominantly generated in the cytosol, with minor GST activities in the nucleus, chloroplast, and mitochondrion (Dixon et al, 2002;Dixon and Edwards, 2009).…”