Pumpkin (Cucurbita moschata) is an important cucurbit vegetable crop that has strong resistance to abiotic stress. While heat shock protein 20 (HSP20) has been implicated in vegetable response to heat stress, little is known regarding activity of HSP20 family proteins in C. moschata. Here, we performed a comprehensive genome-wide analysis to identify and characterize the functional dynamics of the Cucurbita moschata HSP20 (CmoHSP20) gene family. A total of 33 HSP20 genes distributed across 13 chromosomes were identified from the pumpkin genome. Our phylogenetic analysis determined that the CmoHSP20 proteins fell into nine distinct subfamilies, a division supported by the conserved motif composition and gene structure analyses. Segmental duplication events were shown to play a key role in expansion of the CmoHSP20 gene family. Synteny analysis revealed that 19 and 18 CmoHSP20 genes were collinear with those in the cucumber and melon genomes, respectively. Furthermore, the expression levels of pumpkin HSP20 genes were differentially induced by heat stress. The transcript level of CmoHSP20-16, 24 and 25 were down-regulated by heat stress, while CmoHSP20-7, 13, 18, 22, 26 and 32 were up-regulated by heat stress, which could be used as heat tolerance candidate genes. Overall, these findings contribute to our understanding of vegetable HSP20 family genes and provide valuable information that can be used to breed heat stress resistance in cucurbit vegetable crops.

Heat shock protein 90 (HSP90) plays critical roles in plant growth and development, as well as in response to abiotic stresses such as heat and cold. To comprehensively analyze the HSP90 gene family and determine the key HSP90 gene responsive to temperature stress in pumpkin (Cucurbita moschata Duch.), bioinformatics and molecular biology techniques were used in this study. A total of 10 CmoHSP90 genes were identified from the pumpkin genome, encoding amino acids of 567–865, with protein molecular weight of 64.32–97.36 kDa. Based on the phylogenetic analysis, they were classified into four groups. The members in each group contained similar conserved motifs and gene structures. The 10 CmoHSP90 genes were distributed on the 9 chromosomes of C. moschata. Four pairs of segmental duplication genes (CmoHSP90-1/CmoHSP90-10, CmoHSP90-2/CmoHSP90-7, CmoHSP90-3/CmoHSP90-6, and CmoHSP90-4/CmoHSP90-9) were detected. Synteny analysis revealed that 10 C. maxima HSP90 genes and 10 C. moschata HSP90 genes were orthologous genes with 17 syntenic relationships. Promoter analysis detected 23 cis-acting elements including development-, light-, stress-, and hormone-related elements in the promoter regions of pumpkin HSP90 genes. Further analysis showed that the transcript levels of CmoHSP90-3 and CmoHSP90-6 were remarkably up-regulated by heat stress, while CmoHSP90-6 and CmoHSP90-10 were significantly up-regulated by cold stress, suggesting that these HSP90 genes play critical roles in response to temperature stress in pumpkins. The findings will be valuable for understanding the roles of CmoHSP90s in temperature stress response and should provide a foundation for elucidating the function of CmoHSP90s in C. moschata.

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