Identification of CmLEA gene family and mining of abiotic stress resistant genes in melon

【Objective】 To identify and analyze members of the late embryogenesis abundant（LEA） protein gene family in melon,mine the abiotic stress resistant genes,which could provide theoretical foundation for investigating the role of CmLEA gene family in abiotic stress responses and breeding of stress resistant melon varieties.MethodUsing cold tolerant melon L5283 seedlings as experimental materials.At the 3-leaf-and-1-bud stage,4 abiotic stress treatments were applied:salt stress 300 mmol/L sodium chloride（NaCl）,drought 15% polyethylene glycol（PEG） 6000,low temperature（15 ℃/6℃ day/night,12 h/12 h）,and abscisic acid（ABA）（100 μmol/L）.Based on transcriptomic data from melon seedlings treated by low temperature,CmLEA candidate genes were identified.Chromosomal locations,gene structures,subcellular localization,secondary and tertiary protein structures,phylogenetic relationships,protein interactions,and promoter cis-acting elements were predicted by bioinformatics methods.Real-time fluorescence quantitative PCR was used to detect the expression patterns of CmLEA family genes under different abiotic stresses.Result A total of 5CmLEA candidate genes were identified and named CmLEA1-CmLEA5.The 5 CmLEA family genes were unevenly distributed across 4 chromosomes of melon,they encoded 158-315 amino acids,with Theoretical isoelectric point（pI） of4.47-9.70 and molecular weight of 16.90-32.71 kD.Except CmLEA2 were hydrophobic protein,the others were hydrophilic proteins.Among the 5 CmLEA family proteins,random curl accounted for the highest proportion,followed by extended chain and α-helix,and β-fold accounted for the lowest proportion.The conserved motifs of CmLEA family proteins differed greatly.CmLEA1 and CmLEA2 genes both had 1 exon and no intron;CmLEA3 and CmLEA5 genes contained 4 residues and 2 exons respectively.Phylogenetic analysis showed that CmLEA gene family members were closely related to cucumber,and the similarity was up to 100%.The cis-acting elements of CmLEA family genes were classified into 6 categories,including light response elements,hormone response elements,anaerobic induction elements,low temperature response elements,defense and stress response elements,and MYB binding elements.CmLEA5 protein played a key role in the protein-interaction network and was presumed to be involved in the development of stamens.Real-time fluorescence quantitative PCR showed that the relative expression of CmLEA1 and CmLEA2 were significantly upregulated by low temperature and ABA induction（P＜0.05,the same below）.When melon seedlings were subjected to drought stress and salt stress,the relative expression of CmLEA5 gene reached its peak value at 12 h compared with 0 h,and significantly increased by 214 and 5212 times respectively.Conclusion Five CmLEA gene family members were identified,and their structure and function are diverse.Three genes,which are highly responsive to abiotic stress,are identified:CmLEA1,CmLEA2 and CmLEA5,and they can be used as candidate genes for subsequent studies on the molecular mechanism of response to abiotic stress and selection of melon resistant varieties.