Physiological Responses And Transcriptome Analysis Of Chinese Kale Under High Temperature Stress

Chinese kale(Brassica oleracea var.alboglabra Bailey)is one of the popular leafy vegetables in recent years.With a large area of cultivation in the south of China,it has a high nutritive value and good economic benefit.The high temperature and humid climate in south China has a negative impact on the production and the year-round supply of Chinese kale,resulting in a serious reduction in the quality and yield.Therefore,it is of important significance to study the heat resistance mechanism of Chinese kale and find some crucial heat-resistance genes and proteins for genetice improvement of heat-tolerance.In this study,I screened for heat tolerance from 10 varieties,studied the physiological responses under high temperature stress,and further performed RNA-seq analysis using a heat tolerant variety upon high temperature treatment.Based on the screening of differentially expressed genes related to heat resistance,their expression was further validated using qRT-PCR.The major results were as follows:1.By heat-tolerance scoring,4 representative varieties were selected from 10 different varieties of Chinese kale.2.After the high temperature treatment at 37 ℃ for 1 h,3 h,6 h and 12 h,six physiological parameters in 4 varieties of Chinese kale leaves were determined and no direct association between these parameters and heat tolerance phenotype was observed.3.The relatively heat-resistant variety ‘Xiacui’ was treated by high temperature for 0 h,1 h,3 h,6 h and 12 h,and the samples were subjected to transcriptome sequencing.Compared to the control(0 h),there were 5461,7963,7003 and 11140 significant differentially expressed genes(DEGs)respectively,among which 2132 significant DEGs were shared in all timepoints.4.GO classification analysis showed that most unigenes were associated to the sameitems in the biological process,cellular components and molecular function between samples from 3 h,6 h and 12 h.In KEGG pathway analysis,,three pathways were significantly enriched in 1 h treatment in comparison with the control(0 h),only one enriched in 3 h and 6 h treatment,whereas none enriched in 12 h treatment.5.Some differentially expressed genes were selected for validation by Real-Time quantitative Polymerase Chain Reaction(qRT-PCR),and the results showed that the RNA-seq data were reliable.6.The change of gene expression varies with the high temperature treatment time.In the differentially expressed genes,most of the heat shock proteins(HSPs)and heat shock transcription factors(HSFs)were up-regulated,with the highest expression at 1 h and decreased expression at later timepoints.Taken together,this study concluded that the heat tolerance of Chinese kale varies markedly by genetic background.Six physiological parameters were determined and none of them can be used as a heat–tolerance indicator.The transcriptome sequencing-based analysis of differentially expressed genes has laid a good foundation for future gene cloning,function characterization and application of heat-tolerance genes in Chinese kale.