Abstract
Heat shock protein 90 (HSP90) possesses critical functions in plant developmental control and defense reactions. The HSP90 gene family has been studied in various plant species. However, the HSP90 gene family in cucumber has not been characterized in detail. In this study, a total of six HSP90 genes were identified from the cucumber genome, which were distributed to five chromosomes. Phylogenetic analysis divided the cucumber HSP90 genes into two groups. The structural characteristics of cucumber HSP90 members in the same group were similar but varied among different groups. Synteny analysis showed that only one cucumber HSP90 gene, Csa1G569290, was conservative, which was not collinear with any HSP90 gene in Arabidopsis and rice. The other five cucumber HSP90 genes were collinear with five Arabidopsis HSP90 genes and six rice HSP90 genes. Only one pair of paralogous genes in the cucumber HSP90 gene family, namely one pair of tandem duplication genes (Csa1G569270/Csa1G569290), was detected. The promoter analysis showed that the promoters of cucumber HSP90 genes contained hormone, stress, and development-related cis-elements. Tissue-specific expression analysis revealed that only one cucumber HSP90 gene Csa3G183950 was highly expressed in tendril but low or not expressed in other tissues, while the other five HSP90 genes were expressed in all tissues. Furthermore, the expression levels of cucumber HSP90 genes were differentially induced by temperature and photoperiod, gibberellin (GA), downy mildew, and powdery mildew stimuli. Two cucumber HSP90 genes, Csa1G569270 and Csa1G569290, were both differentially expressed in response to abiotic and biotic stresses, which means that these two HSP90 genes play important roles in the process of cucumber growth and development. These findings improve our understanding of cucumber HSP90 family genes and provide preliminary information for further studies of cucumber HSP90 gene functions in plant growth and development.
Highlights
Plants are usually exposed to different kinds of environmental stress conditions during their growth and development
The Hidden Markov Model (HMM) profile of the Heat shock protein 90 (HSP90) domain (PF00183) was downloaded from the Pfam database.3. This model was used as a query to search for HSP90 proteins in the eight Cucurbitaceae crop protein files based on an expected value (E-value) cutoff of 1 × 10−5 in HMMER 3.0 (Finn et al, 2011)
The results revealed that five cucumber HSP90 genes and five Arabidopsis HSP90 genes were orthologous genes with seven syntenic relationships
Summary
Plants are usually exposed to different kinds of environmental stress conditions during their growth and development. With the continuous development of global warming, high temperature stress has become one of the main factors affecting the normal growth and development of plants (Ahuja et al, 2010). Under the condition of high temperature stress, the organisms will activate and accumulate a large amount of the HSPs to participate in the heat shock response to maintain the stability of cells (Richter et al, 2010). HSP90 is a heat shock protein family with a molecular weight of about 90 kD, which is composed of three structural domains, including the N-terminal region containing ATP binding and hydrolysis sites, the middle region (M) and the C-terminal region containing dimerization regions (Rizzolo et al, 2014). HSP90 is an abundant and highly conserved molecular chaperone that is essential for viability in eukaryotes, which fulfills housekeeping functions on important biological processes such as signal transduction and cell cycle (Johnson and Brown, 2009)
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