Genome-Wide Characterization of HSP90 Gene Family in Chinese Pumpkin (Cucurbita moschata Duch.) and Their Expression Patterns in Response to Heat and Cold Stresses

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.