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

Abstract

Plant growth and development can be adversely affected by cold stress, limiting productivity. The glutathione <i>S</i>-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 (<i>Cucurbita</i><i>maxima</i>) 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 <i>C. maxima GST</i> (<i>CmaGST</i>) genes using a combination of bioinformatics approaches and characterized them by expression profiling. These <i>CmaGST</i> genes represent seven of the 14 known classes of plant <i>GSTs</i>, with 18 <i>CmaGST</i>s categorized into the tau class. The <i>CmaGST</i>s were distributed across 13 of pumpkin's 20 chromosomes, with the highest numbers found on chromosomes 4 and 6. The large number of <i>CmaGST</i> genes resulted from gene duplication; 11 and 5 pairs of <i>CmaGST</i> genes were segmental- and tandem-duplicated, respectively. In addition, all <i>CmaGST</i> genes showed organ-specific expression. The expression of the putative <i>GST</i> genes in pumpkin was examined under cold stress in two lines with contrasting cold tolerance: cold-tolerant CP-1 (<i>C. maxima</i>) and cold-susceptible EP-1 (<i>Cucurbita moschata</i>). Seven genes (<i>CmaGSTU3</i>, <i>CmaGSTU7</i>, <i>CmaGSTU8</i>, <i>CmaGSTU9</i>, <i>CmaGSTU11</i>, <i>CmaGSTU12</i>, and <i>CmaGSTU14</i>) 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.