Genome-Wide Identification, Characterization, and Expression Profiling of Glutathione S-Transferase (GST) Family in Pumpkin Reveals Likely Role in Cold-Stress Tolerance.

Md Abdul Kayum,Jae-Young Song,Eung Choi,Ujjal Nath,Ill-Sup Nou,Hoy-Taek Kim,Manosh Biswas,Jong-In Park

doi:10.3390/genes9020084

Abstract

Plant growth and development can be adversely affected by cold stress, limiting productivity. The glutathione S-transferase (GST) family comprises important detoxifying enzymes, which play major roles in biotic and abiotic stress responses by reducing the oxidative damage caused by reactive oxygen species. Pumpkins (Cucurbita maxima) are widely grown, economically important, and nutritious; however, their yield can be severely affected by cold stress. The identification of putative candidate genes responsible for cold-stress tolerance, including the GST family genes, is therefore vital. For the first time, we identified 32 C. maxima GST (CmaGST) genes using a combination of bioinformatics approaches and characterized them by expression profiling. These CmaGST genes represent seven of the 14 known classes of plant GSTs, with 18 CmaGSTs categorized into the tau class. The CmaGSTs were distributed across 13 of pumpkin’s 20 chromosomes, with the highest numbers found on chromosomes 4 and 6. The large number of CmaGST genes resulted from gene duplication; 11 and 5 pairs of CmaGST genes were segmental- and tandem-duplicated, respectively. In addition, all CmaGST genes showed organ-specific expression. The expression of the putative GST genes in pumpkin was examined under cold stress in two lines with contrasting cold tolerance: cold-tolerant CP-1 (C. maxima) and cold-susceptible EP-1 (Cucurbita moschata). Seven genes (CmaGSTU3, CmaGSTU7, CmaGSTU8, CmaGSTU9, CmaGSTU11, CmaGSTU12, and CmaGSTU14) were highly expressed in the cold-tolerant line and are putative candidates for use in breeding cold-tolerant crop varieties. These results increase our understanding of the cold-stress-related functions of the GST family, as well as potentially enhancing pumpkin breeding programs.

Highlights

The glutathione S-transferases (GSTs, EC 2.5.1.18) are a large and complex enzyme family, involved in key metabolic steps in many eukaryotic organisms [1,2,3], including catalyzing the nucleophilicGenes 2018, 9, 84; doi:10.3390/genes9020084 www.mdpi.com/journal/genesGenes 2018, 9, 84 conjugation of the reduced site-specific (G-site) tri-peptide into a wide range of electrophilic and hydrophobic substrates, as well as redox buffering
The coding sequence (CDS) and protein sequences of the putative GST family members were extracted from the cucurbit genomic database, and the protein sequences were further examined to confirm the presence of the GST-N
We identified GST genes from the cucurbit and National Center for Biotechnology Information (NCBI) databases using the key word “GST”

Summary

Introduction

The glutathione S-transferases (GSTs, EC 2.5.1.18) are a large and complex enzyme family, involved in key metabolic steps in many eukaryotic organisms [1,2,3], including catalyzing the nucleophilicGenes 2018, 9, 84; doi:10.3390/genes9020084 www.mdpi.com/journal/genesGenes 2018, 9, 84 conjugation of the reduced site-specific (G-site) tri-peptide (glutathione, GSH, and Glu-Cys-Gly) into a wide range of electrophilic and hydrophobic substrates, as well as redox buffering. GSTs play vital roles in the detoxification of xenobiotics and toxic lipid peroxides [4,5], signal transduction, protection against damage from ozone, heavy metals [6], and glucosinolate biosynthesis and metabolism [7]. They act as non-catalytic carrier proteins, which are required for vacuolar uptake of anthocyanins [8,9] and the regulation of plant growth and development [10]. The secondary structure analysis of the GSTs suggests that α-helix is the predominant structure followed by random coil and β-sheet in most of the plant GSTs [13]

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Discussion

Conclusion