Transcriptome And Metabolome Analysis Of Pumpkin Response To Low Temperature Stress

When plants are exposed to low temperature stress during growth and development,it will cause metabolic disorders and even caused death.So that,how to screen and improve varieties with low temperature resistance which always has been an important problem to be solved urgently.Pumpkins especially like warm environments,the consequences are seriously when it suffers from low temperature stress.Therefore,we study the low temperature tolerance mechanism of pumpkin.It's of great significance for breeding and screening low temperature resistant pumpkin varieties.In our study,we identified the low temperature tolerance ability of 19 pumpkin varieties during germination,and identified low temperature sensitive inbred lines(IL1)and low temperature resistant inbred lines(IL7)for subsequent experiments.When the seedlings reach three leaves treated at 5?for 24 h.The cold damage index was evaluated by observing the phenotype of pumpkin seedlings,and measured the physiological and biochemical indexes of young leaves.Then combined the sequencing results of the transcriptome and metabolome,to studied the low temperature tolerance mechanism of two pumpkin inbred lines.The test results are as follows:(1)Observe the result of relative germination rate,relative germination potential,and relative germination index.It shows that IL1 seeds have lower low temperature tolerance during germination,while IL7 seeds have stronger low temperature tolerance during germination.(2)Compared with IL7,the young leaves of IL1 wilted and curled more seriously,and the water-stained spots on the leaf surface were more obvious.All in all,the low temperature injury of IL 1was more obvious.The chilling injury index showed that IL1 had weak low-temperature resistance and IL7 had medium low-temperature resistance.which was consistent with the results of low temperature tolerance identification during germination.Compared with the control group,the relative conductivity and soluble protein content of IL1 and IL7 increased significantly;the chlorophyll content of IL1and IL7 reduced significantly;the soluble sugar content and hydrogen peroxide activity of IL7 increased significantly,but IL1 didn't change significantly;the activities of superoxide dismutase and peroxidase of IL1 decreased significantly,while IL7 didn't change significantly;the malondialdehyde content of IL1 increased significantly,while IL7 didn't change significantly.Physiological changes indicate that IL7 is more resistant to low temperature than IL1.(3)Transcriptome analysis showed that 5869 and 5553 DEGs were identified in IL1 and IL7,respectively.The GO entries were significantly enriched in IL1 and IL7as follows:nucleus,DNA binding transcription factor activity,apoplast,plant-type cell wall,and expression trends show similar distribution patterns.There were 124 and 120Pathway pathways enriched in IL1 and IL7,and there were 115 common pathways.Low temperature stress mainly affected the metabolism,genetic information,biological systems and signal transduction of IL1 and IL7.Both of them were enriched in plant hormone signal transduction,and the transcription factor family has a significant resistance to low temperature stress.It was verified by qRT-PCR that the gene expression was strongly positively correlated with the transcriptome(R~2=0.9631).(4)Metabolomics analysis showed that there were 178 and 114 differentially expressed metabolites in IL1 and IL7,respectively.Further analysis of the significantly different metabolic pathways and differential metabolites found that differential metabolites were mainly concentrated in amino acid substances,sugars and sugar derivatives.In the differential metabolic pathways of amino acids,IL1 has down-regulated metabolites such as proline and methionine,and IL7 has no down-regulated expression of amino acids;IL1 and IL7 in the differential metabolic pathway of sugars and sugar derivatives have down-regulated and up-regulated sugar metabolites.In the differential metabolic pathways of sugars and sugar derivatives,IL1and IL7 has down-regulate and up-regulate carbohydrate metabolites,respectively.After low temperature treatment,the gene expression and metabolite levels between two pumpkin inbred lines were highly matched with physiological indicators results.It helped us understand the low temperature tolerance mechanism of pumpkins and provide a basis for evaluating and breeding low temperature resistant strains.