Identification and analysis of HSP90 genes in papaya (Carica papaya L.) by using bioinformatics method

The HSP90 gene family has been shown to play an important role in the tolerance and development of plants. Papaya, which is a fruit crop with high nutritional value, is native to the tropics but now is widely cultivated in many subtropical regions of the world. Therefore, papaya plants have to face many environmental factors during their life. This study aims to identify and analyze the HSP90 gene family in papaya by bioinformatics method. A total of seven HSP90 genes have been identified in the genome of papaya (Carica papaya L.) by using the bioinformatic methods. The full-length genomic sequence of papaya HSP90 genes were ranging from 2650 to 8136 nucleotides, non continuous coding, with number of intro ranging from two to 19. The predicted protein sequences included from 348 to 796 amino acids, according to the molecular weight ranged from 39.92 to 90.61 kDa. Among seven CpHSP90, the two CpHSP90-1 and CpHSP90-4 were considered pseudogenes due to their small size. These proteins were acidic with a pI value ranging from 4.69 to 5.42, except CpHSP90-1 (pI 7.03). Based on the protein structure, subcellular localization and the phylogenic analysis, the papaya HSP90 were divided into two groups, I (cytoplasmic HSP90, four members) and II (organelle HSP90, three members). Analysis of transcriptomes showed that the papaya HSP90s were differentially expressed in different tissues at different development stages. In which, most of the papaya HSP90 is highly expressed in flower buds or in fruits at stage 2 or stage 3. CpHSP90-2 had the highest level of expression, followed by CpHSP90-5. In contrast, CpHSP90-1 was not expressed or very weakly expressed in these studied tissues. All of seven HSP90 genes of papaya were induced by freeze-thaw awakening treatment (in comparison with control treatment), among them, CpHSP90-1 was strongest induced by stress (12.13-folds), however, it was a pseudogene and had a very low level of basal expression. CpHSP90-2 had a high induction level (2.81- folds), and also had a high basal expression level compared to other HSP90 genes of papaya. The results of this work have an important significance and will serve as a base for the further research on gene cloning, functional analysis of HSP90 genes and breeding of papaya in response to environmental abiotic stresses and the development of this fruit crop.