Transcriptome Analysis Of Responding To Low Temperature In Melon (Cucumis Melo L.)

Low temperature is a one of major limiting factors of melon production in northern cold regions,therefore,studies on response mechanisms of plants to cold stress are very important.It will not only provide a guide to cultivation in early spring,but also help to breed cold tolerance of other cucubit plants and increase yield.Two cultivars were used in this experiment,which were cold-tolerance melon X207 and cold-sensitive melon M4-117.Under 4℃ low temperature stress,phenotypic observation,determination of relevant physiological and biochemical indexes,transcriptome analysis were carried out in two melons.The main results were as following:1.X207 and M4-117 showed different cold tolerance on phenotypic changes.The content of MDA and pro,activities of SOD and POD in both species showed a significant change under cold stress.X207 showed a better adaptability for cold stress with low MDA content、high SOD and CAT activity and pro content than M4-117.These results showed that X207 had good cold resistance.2.Transcriptome sequence was implemented in seedling stage of two melon cultivars at 0 h,8h and 72 h after 4℃ treatment by illumina Hi-seq-2000 sequencing platform,and their sequence data were analyzed.In X207,1277(841 up-regulated and 436 down-regulated)and 2393(1254 up-regulated and 1139 down-regulated)DEGs were found at 8h and 72 h after cold stress,respectively.In M4-117,1571(1040 up-regulated and 531 down-regulated)and 3761(1637 up-regulated and 2124 down-regulated)DEGs were found at 8h and 72 h after cold stress,respectively.3.A total 5633 DEGs annotated into 31 GO terms of three catalogues.In cellular component catalogue,most DEGs belonged three GO terms of nucleus,plasma membrane and mitochondrion.In biological process catalogue,most DEGs belonged three GO terms of oxidation reduction process,protein phosphorylation and transcriptional regulation.In molecular function catalogue,most DEGs belonged three GO terms of ATP binding,nucleotide binding and DNA binding.The comparison results of DEGs with KEGG database showed that 1593 DEGs were significantly enriched in 121 pathways.DEGs of carbohydrate metabolism,amino acid metabolism and signal transduction pathways had the greatest proportion.4.The DEGs were analysed,which belonged ABA signaling pathway,stress proteins and transcription factors.Nineteen candidate genes for cold tolerance were screened,including 1 PYR,1 PYL,9 PP2 C,4 RK2 s,1 DHN1,1 GLP,2 HSP genes and WRKY、bHLH、NAC、AP2/ERF transcription factor families et al.And DEGs of metabolic and regulatory pathways were discussed,thus laying a foundation for further functional identification of the target gene.It would provide important reference for further molecular breeding of muskmelon cold resistance.5.The 12 differentially expressed genes were verified by real-time quantitative PCR.The results showed that the quantitative results were same with transcriptome sequencing results,demonstrating the accuracy of transcriptome sequencingSix genes related to low temperature tolerance were identified,which were phospholipid-transporting ATPase 9、V-type proton ATPase catalytic subunit A、ferredoxin-like、chlorophy II a-b binding protein、heat shock protein and AP2/EREBP.