Genome-Wide Identification and Expression Analysis of Heat Shock Protein 70 (HSP70) Gene Family in Pumpkin (Cucurbita moschata) Rootstock under Drought Stress Suggested the Potential Role of these Chaperones in Stress Tolerance

Abstract

Heat shock protein 70s (HSP70s) are highly conserved proteins that are involved in stress responses. These chaperones play pivotal roles in protein folding, removing the extra amounts of oxidized proteins, preventing protein denaturation, and improving the antioxidant system activities. This conserved family has been characterized in several crops under drought stress conditions. However, there is no study on HSP70s in pumpkin (Cucurbita moschata). Therefore, we performed a comprehensive analysis of this gene family, including phylogenetic relationship, motif and gene structure analysis, gene duplication, collinearity, and promoter analysis. In this research, we found 21 HSP70s that were classified into five groups (from A to E). These genes were mostly localized in the cytoplasm, chloroplast, mitochondria, nucleus, and endoplasmic reticulum (ER). We could observe more similarity in closely linked subfamilies in terms of motifs, the number of introns/exons, and the corresponding cellular compartments. According to the collinearity analysis, gene duplication had occurred as a result of purifying selection. The results showed that the occurrence of gene duplication for all nine gene pairs was due to segmental duplication (SD). Synteny analysis revealed a closer relationship between pumpkin and cucumber than pumpkin and Arabidopsis. Promoter analysis showed the presence of various cis-regulatory elements in the up-stream region of the HSP70 genes, such as hormones and stress-responsive elements, indicating a potential role of this gene family in stress tolerance. We furtherly performed the gene expression analysis of the HSP70s in pumpkin under progressive drought stress. Pumpkin is widely used as a rootstock to improve stress tolerance, as well as fruit quality of cucumber scion. Since stress-responsive mobile molecules translocate through vascular tissue from roots to the whole plant body, we used the xylem of grafted materials to study the expression patterns of the HSP70 (potentially mobile) gene family. The results indicated that all CmoHSP70s had very low expression levels at 4 days after stress (DAS). However, the genes showed different expression patterns by progressing he drought period. For example, the expression of CmoHSP70-4 (in subgroup E) and CmoHSP70-14 (in subgroup C) sharply increased at 6 and 11 DAS, respectively. However, the expression of all genes belonging to subgroup A did not change significantly in response to drought stress. These findings indicated the diverse roles of this gene family under drought stress and provided valuable information for further investigation on the function of this gene family, especially under stressful conditions.

Genome-Wide Identification and Characterization of Chinese Cabbage S1fa Transcription Factors and Their Roles in Response to Salt Stress

“…Interestingly, based on motif analysis, the S1fa genes in Chinese cabbage can be divided into two subgroups, with Bra003132 and Bra006994 in one group, and Bra029784 and Bra034084 in the other ( Figure 4 ). Protein analysis shows that motif 1 is highly conserved, which may be involved in or required for recognizing abiotic stress responsive cis-elements in response to stresses [ 31 , 32 , 33 ].…”

“…The online tool PlantCARE ( (accessed on 22 March 2022)) was used to analyze the cis-elements in the promoter sequence [ 17 ]. To predict the miRNAs, the coding sequence of the S1fa genes was submitted to the psRNATarget server ( (accessed on 22 March 2022)) as the targeted candidate as described previously [ 32 ].…”

Genomic Survey of Heat Shock Proteins in Liriodendron chinense Provides Insight into Evolution, Characterization, and Functional Diversities

“…It exists mainly as a homodimer, containing a 12 kDa N-terminal domain of the ATP-binding site, the 35 kDa intermediate domain, and a 25 kDa C-terminal substrate-binding domain [ 13 , 14 ]. The HSP70 class is one of the most widely distributed and studied heat shock proteins, comprising of a 44 kDa N-terminal ATP binding domain (NBD), 15 kDa substrate binding domain, and about 10 kDa C-terminal domain [ 15 , 16 ]. It is also found that HSP70 family is highly homologous to HSP110 family, showing similarity in gene sequence and structural characteristics.…”

Comparative Transcriptome Analysis of Grafted Tomato with Drought Tolerance

“…For example, HSP70 in cucumber ( Cucumis sativus L.) was induced by a stress-tolerant rootstock pumpkin ( Cucurbita moschata ) and luffa ( Luffa cylindrica Roem. ) through ABA-dependent activation [ 27 , 28 ]. As the result shown in Table 1 and Figure 3 b, the graft strongly activated several ABA-related genes.…”