Abstract
Glyoxalase is an evolutionary highly conserved pathway present in all organisms. Conventional glyoxalase pathway has two enzymes, glyoxalase I (GLYI) and glyoxalase II (GLYII) that act sequentially to detoxify a highly cytotoxic compound methylglyoxal (MG) to D-lactate with the help of reduced glutathione. Recently, proteins with DJ-1/PfpI domain have been reported to perform the same conversion in a single step without the help of any cofactor and thus termed as “unique glyoxalase III” enzyme. Genome-wide analysis of glyoxalase genes have been previously conducted in Arabidopsis, rice and Soybean plants, but no such study was performed for one of the agricultural important model legume species, Medicago truncatula. A comprehensive genome-wide analysis of Medicago identified a total of putative 29 GLYI, 14 GLYII genes, and 5 glyoxalase III (DJ-1) genes. All these identified genes and their corresponding proteins were analyzed in detail including their chromosomal distribution, gene duplication, phylogenetic relationship, and the presence of conserved domain(s). Expression of all these genes was analyzed in different tissues as well as under two devastating abiotic stresses- salinity and drought using publicly available transcript data. This study revealed that MtGLYI-4, MtGLYII-6, and MtDJ-1A are the constitutive members with a high level of expression at all 17 analyzed tissues; while MtGLYI-1, MtGLYI-11, MtGLYI-5, MtGLYI-7, and MtGLYII-13 showed tissue-specific expression. Moreover, most of the genes displayed similar pattern of expression in response to both salinity and drought stress, irrespective of stress duration and tissue type. MtGLYI-8, MtGLYI-11, MtGLYI-6, MtGLYI-16, MtGLYI-21, and MtGLYII-9 showed up-regulation, while MtGLYI-17 and MtGLYI-7/9 showed down-regulation in response to both stresses. Interestingly, MtGLYI-14/15 showed completely opposite pattern of expression in these two stresses. This study provides an initial basis about the physiological significance of glyoxalase genes in plant development and stress response of Medicago that could be explored further.
Highlights
Glyoxalase pathway is one of the evolutionary highly conserved pathways which have been found in all era of organisms starting from lower prokaryotic Escherichia coli to higher eukaryotes Homo sapiens (Kaur et al, 2014a)
Putative Medicago glyoxalase I (GLYI), glyoxalase II (GLYII) and unique Glyoxalase III (GLYIII) (DJ-1) proteins were identified by BLASTP search at JCVI M. truncatula annotation database 4.0v11 (Young et al, 2011) with an e-value of 1 using previously reported Arabidopsis GLYI (GenBank: AEE28797.1), Brassica GLYII (GenBank: AAO26580.1) and rice DJ-1C (LOC_Os04g57590) protein sequence as query, respectively
Both the number of GLYII genes and proteins were found to be greater than previously reported Arabidopsis (5 genes and 9 proteins), rice (3 genes and 4 proteins), and soybean (12 genes and 23 proteins) (Mustafiz et al, 2011; Ghosh and Islam, 2016)
Summary
Glyoxalase pathway is one of the evolutionary highly conserved pathways which have been found in all era of organisms starting from lower prokaryotic Escherichia coli to higher eukaryotes Homo sapiens (Kaur et al, 2014a). Glyoxalase pathway detoxifies highly cytotoxic compound MG into its non-toxic form, Dlactate (Figure 1). Conventional glyoxalase pathway consists of two enzymes; GLYI and GLYII (Kaur et al, 2014c). MG and GSH generate a non-enzymatic adduct hemithioacetal (HTA). GLYI isomerizes HTA to S-lactyl-glutathione (SLG) which is further hydrolysed by GLYII into D-lactate and GSH (Figure 1). There are some reports of the presence of another unique glyoxalase member named Glyoxalase III (GLYIII) (Lee et al, 2012; Kwon et al, 2013; Ghosh et al, 2016). GLYIII could do the same conversion of MG into D-lactate in a single step (Figure 1)
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