Identification and expression analysis during ovule development of Hsp90 gene family in Castanea mollissima

  Objective  Recent studies have found that Hsp90 gene family is related to embryo development, but the details of Hsp90 gene family in chestnut are not clear. The identification and analysis of Hsp90 gene family in chestnut provide a theoretical basis for studying the function of Hsp90 gene family and its role in pollination, fertilization and ovule development, so as to improve the yield of chestnut.

  Method  The members of chestnut Hsp90 gene family were identified by bioinformatics. The physical and chemical properties, gene structure, evolutionary relationship and promoter elements of the family members were analyzed. The expression of CmHsp90 genes at different developmental stages of ovule was analyzed based on transcriptome data.

  Result  A total of 10 CmHsp90 genes were identified in Chinese chestnut. The length of CDS of 10 CmHsp90 gene family members ranged from 2 112 to 2 481 bp, the number of amino acids encoded ranged from 703 to 826. The relative molecular weight ranged from 80.67 to 94.21 kDa, and the pI ranged from 4.81 to 5.26 kDa. The coefficient of instability ranged from 36.15 to 46.75. Except CmHsp90-6, CmHsp90-4 and CmHsp90-9, the proteins encoded by other genes were relatively stable. According to the subcellular localization prediction of CmHsp90 family protein members, five members (CmHsp90-1, CmHsp90-4, CmHsp90-5, CmHsp90-9 and CmHsp90-10) were located in the cytoplasm, two members (CmHsp90-7 and CmHsp90-8) were located in the endoplasmic reticulum, and the other three members were located in the nucleus (CmHsp90-3), mitochondria (CmHsp90-2) and chloroplast (CmHsp90-6). By predicting the signal peptide of CmHsp90 gene family proteins, it was found that only CmHsp90-7 and CmHsp90-8 had potential signal peptide sites. The motif and protein domains of CmHsp90 gene family proteins were basically the same, including Hsp90 domain (PF00183) and HATPase_c domain (PF02518). Based on phylogenetic tree analysis, 10 CmHsp90 proteins were divided into 5 groups. The cis acting elements in the promoter region of CmHsp90 gene family were predicted. It was found that the light response element was the main regulatory element on the promoter of CmHsp90 gene family, followed by ABA response element. In addition, four genes (CmHsp90-1, CmHsp90-5, CmHsp90-7, CmHsp90-8) had temperature response elements. By analyzing the RNA-seq data of ovules at different developmental stages, it was found that the expression of other genes in ovules before fertilization was higher than that after fertilization, except CmHsp90-3 gene; the expression of CmHsp90-2, CmHsp90-4, CmHsp90-5, CmHsp90-7, CmHsp90-8, CmHsp90-9 and CmHsp90-10 genes in developing ovules was higher than that in abortive ovules.

  Conclusion  The CmHsp90 genes in chestnut were identified and analyzed for the first time. The results show that the expression of Hsp90 genes is different in varied ovule development processes, and the expression in developing ovules and abortive ovules in the same ovary is also different. The research results lay a foundation for the further study of the specific role of CmHsp90 gene in chestnut pollination, fertilization and embryo abortion.