Transcriptomic mechanism revealed IbGST4 and IbGST2 genes response to low-temperature stress in sweet potatoes

Sweet potato (Ipomoea batatas L.) is a crop native to the tropics that is weakly resistant to cold. Low temperatures are important factors limiting its storage. By analyzing the phenotypic and tuberous root color differences between Xushu 32 and Yanshu 25 under low-temperature treatment, we found that Xushu 32 showed less low-temperature damage. Transcriptome analysis was performed on the tuberous roots of the two sweet potatoes at different storage times to further investigate the molecular mechanism. There were 7039 differentially co-expressed genes in Xushu 32 and 11033 differentially co-expressed genes in Yanshu 25 after 4 and 8 days of low-temperature treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that the percentage of differentially expressed genes in the glutathione metabolism pathway in Xushu 32 was significantly higher than that in Yanshu 25. Weighted correlation network analysis (WGCNA) analysis indicated that the expression modules of MElightcyan1 and MEmegenta3 were up-regulated under low-temperature stress and that glutathione S-transferases (GSTs) were hub genes with high connectivity. The candidate genes IbGST2 and IbGST4 were highly similar to a rice glutathione S-transferase (GST) (Os10g0528900) by heatmap analysis and evolutionary tree analysis and may play a role in low-temperature stress. Subsequently, gene-silenced plants of the homologous genes SlBI-GST and SlGST-T4 in tomatoes were constructed using virus-induced gene silencing (VIGS) technology, and the contents of reactive oxygen species (ROS) metabolites and expression of BI-GST, GST-T4, and the C-repeat binding transcription factors (CBFs) were determined. This suggested that BI- GST and GST- T4 genes could scavenge ROS and improve the cold tolerance of tomatoes. These results provide important insights into the roles of IbGST2 and IbGST4 in the storage characteristics of sweet potatoes under low-temperature stress.