As a group of multifunctional enzymes, glutathione S-transferases (GSTs) participate in oxidative stress resistance and cellular detoxification. Here, we identified 39 CmGST genes with typical binding sites from the Hami melon genome, and they can be classified into seven subfamilies. Their molecular information, chromosomal locations, phylogenetic relationships, synteny relationships, gene structures, protein–protein interactions, structure of 3-D models, and expression levels under cold stress were analyzed. Expression analysis indicates that cold-tolerant Jia Shi-310 (JS) had higher GST enzyme activities and expression levels of 28 stress-related genes under cold stress. Some CmGSTs belonging to Tau, Phi, and DHAR classes play significant roles under cold stress, and they could be regarded as candidate genes for further studies. The present study systematically investigated the characterization of the Hami melon GST gene family, extending our understanding of Hami melon GST mediated stress-response mechanisms in this worldwide fruit.

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Background: Cantaloupe is susceptible to cold stress when it is stored at low temperatures, resulting in the loss of edible and commercial quality. To ascertain the molecular mechanisms of low temperatures resistance in cantaloupe, a cold-sensitive cultivar, Golden Empress-308 (GE) and a cold-tolerant cultivar, Jia Shi-310 (JS), were selected in parallel for iTRAQ quantitative proteomic analysis. Results: The two kinds of commercial cultivars were exposed to a temperature of 0.5°C for 0, 12 and 24 days. We found that the cold-sensitive cultivar (GE) suffered more severe damage as the length of the cold treatment increased. Proteomic analysis of both cultivars indicated that the number of differentially expressed proteins (DEPs) changed remarkably during the chilly treatment. JS expressed cold-responsive proteins more rapidly and mobilized more groups of proteins than GE. Furthermore, metabolic analysis revealed that more amino acids were up-regulated in JS during the early phases of low temperatures stress. The DEPs we found were mainly related to carbohydrate and energy metabolism, structural proteins, reactive oxygen species scavenging, amino acids metabolism and signal transduction. The consequences of phenotype assays, metabolic analysis and q-PCR validation confirm the findings of the iTRAQ analysis. Conclusion: We found that the prompt response and mobilization of proteins in JS allowed it to maintain a higher level of cold tolerance than GE, and that the slower cold responses in GE may be a vital reason for the severe chilling injury commonly found in this cultivar. The candidate proteins we identified will form the basis of future studies and may improve our understanding of the mechanisms of cold tolerance in cantaloupe.

Background: During the low temperature storage, cantaloupe is susceptible to the cold stress, resulting in the loss of edible and commercial quality. To ascertain the molecular mechanisms of cold tolerance in cantaloupe, cold-sensitive cultivar Goldqueen-308 (GE) and cold-tolerant cultivar Jiashi-310 (JS) were used for quantitative proteomic analysis with iTRAQ in parallel. Results: In this work, two commercial cultivars were treated at 0.5℃ for 0, 12 and 24 days. Phenotypes assays showed that GE suffered a more severe damage as the cold treatment time extended. Proteomic analysis revealed that the number of differentially expressed proteins (DEPs) changed significantly over time in cold-exposed cantaloupe. Comparing with GE, JS responded in a prompter manner in terms of expressing cold-responding proteins during the similarly cold treatment. Furthermore, much more different groups of proteins were mobilized in response to the cold treatment in JS comparing with GE. Metabolic analysis indicated that more amino acids were up-regulated in JS during the early phases of cold stress. This study also identified some DEPs since they were up-regulated in JS or down-regulated in GE in terms of molecular mechanisms, which were mainly related to carbohydrate and energy metabolism, structure proteins, ROS scavening, amino acid metabolic and signaling transduction. Moreover, iTRAQ analysis was confirmed to be reliable via the results of phenotypes assays, metabolic analysis and q-PCR validation. Conclusion: By proteomics information,we found that the prompt response and the significant mobilization of proteins in JS maintained a higher level of cold tolerance, and the delay of cold response in GE could be a critical reason for the severe chilling injury. The candidate proteins we found will be the basis of future studies for further investigations and our findings may help to better understand the novel mechanisms of cold tolerance in cantaloupe.

ABSTRACT. The high-affinity K + transporter (HKT) family comprises a group of multifunctional cation transporters widely distributed in organisms ranging from Bacteria to Eukarya. In angiosperms, the HKT family consists primarily of nine types, whose evolutionary relationships are not fully understood. The available sequences from 31 plant species were used to perform a comprehensive evolutionary analysis, including an examination of selection pressure and estimating phylogenetic tree and gene duplication events. Our results show that a gene duplication in the HKT1;5/HKT1;4 cluster might have led to the divergence of the HKT1;5 and HKT1;4 subfamilies. Additionally, maximum likelihood analysis revealed that the HKT family has undergone a strong purifying selection. An analysis of the amino acids provided strong statistical evidence for a functional divergence between subfamilies 1 and 2. Our study was the first to provide evidence of this functional divergence between these two subfamilies. Analysis of co-evolution in HKT identified 25 co-evolved groups. These findings expanded our understanding of the evolutionary mechanisms driving functional diversification of HKT proteins.