| Peach(Prunus persica)trees were grown originally in China,which is one of the main cultivated fruits in China.At present,more than 80% varieties used in production are independent breeding varietiy of China.However,cultivated varieties often suffer from freezing damage in cold areas.Temperature becomes the key factor restricting the overwintering safty of peach trees.Gansu province is one of the original areas of peach,and also an important region for peach germplasm resources conservation,evolution and cultivation.The winter of Hexi Corridor region of Gansu is long and cold,where the soil freezing time is long.The average absolute minimum temperature is about-30℃ of this region.A lot of peach resources with strong cold resistance were selected under long-term natural selection and artificial cultivation under these environmental conditions.Gansu local peach resources is a valuable germplasm material for peach variety improvement and resistance breeding.In this study,physiological and biochemical indexes under low temperature stress(-5℃ control,-10℃,-15℃,-20℃,-25℃,-30℃,-35℃ and-40℃)were used to determine the physiological and biochemical response under low temperature stress of peach.Meanwhile,the relationship between ecological adaptability and cold resistance of peach was analyzed by microscopic observation of anatomical structure sections of leaves and branches.The cold resistance of 28 resources(varieties)was evaluated by the method of membership function.The strongest cold resistance were selected.High-throughput sequencing was used to analyze the molecular response mechanism of local peach resources in Gansu province at the transcriptome level,and qRT-PCR was used to verify and analyze the candidate differential genes,so as to further analyze the cold resistance mechanism of local peach resources in Gansu province.The main research results are as follows:1.9 peach varieties of different ecological cultivation areas and different types are choosing to analyze the physiological response under low temperature stress.The electrical conductivity of annual branches under low temperature stress increased with the decrease of temperature,showing an S-shaped curve.The electrical conductivity was measured and the change curve was fitted with the Logistic equation to obtain the semi-lethal temperature(LT50)of each variety.LT50 can be used as an important index for the cold resistance evaluation of peach tree.LT50 was positively correlated with the electrolyte leakage rate and malondialdehyde(MDA)content,and the correlation coefficients were 0.894 and 0.863,respectively.It was negatively correlated with the contents of soluble sugar(SS),soluble protein(SP)and free proline(Pro),the correlation coefficients were-0.894,-0.721 and-0.863,respectively.There was a significant negative correlation between CAT activity,the correlation coefficient was-0.529.However,the correlation with POD and SOD activity was not significant.Thus REC,SS,SP,MDA,Pro and CAT can all be used as reference indexes for cold resistance evaluation.2.The semi-lethal temperature(LT50)of 20 local peach resources in gansu province and 8 peach varieties ranged from-28.22 ℃ to-17.22 ℃,of which 20 peach LT50 were from-25 ℃ to-20 ℃,accounting for 71.43%.The lowest LT50 resources is Dingjiaba Liguang Tao which was-28.22 ℃.The results of LT50 were basically consistent with the cold resistance of the varieties in the field survey under natural conditions.3.The tissue structure of the leaves of 20 local peach resources and 8 cultivars in growing season(June)and annual branches in dormant period(January)were observed.LT50 of annual branches was negatively correlated with branchxylem thickness,cork layer thickness,cork layer ratio and bark ratio,and the correlation coefficients were-0.694,-0.0.741,-0.822 and-0.814,respectively.There was a significant negative correlation with xylem ratio,the correlation coefficient was-0.678.There was a significant positive correlation with cortical ratio and the correlation coefficient was 0.657.In the branch structure,the ratio of cork layer and the ratio of wood bark were significantly correlated with the cold resistance,and the significance was the highest,which can be used as a reference index of ecological adaptability for the evaluation of peach cold resistance.4.By measuring the physiological and biochemical indexes under the low temperature stress of-25℃ and ecological adaptability indexes of 20 local peach resources and 8 varieties,the membership function method was used to comprehensively evaluate the average membership degree between 0.17 and 0.61,and the average membership degree of Dingjiaba Liguang Tao was 0.61,with the strongest cold resistance.5 Transcriptome of samples treated at-5℃,-15℃,-25℃ and-35℃,respectively,were generated and characterized.Totally,890 differentially expressed genes(DEGs)were identified,including 693 up-regulated and 197 down-regulated.These genes were enriched in 38 Gene Ontology(GO)terms and 24 clusters of orthologous groups(COG)involved in 64 Kyoto Encyclopedia of Genes and Genomes(KEGG)defined pathways.DEGs related to signal transduction,carbohydrates and lipid metabolism were significantly enriched.Totally,124 transcription factors belonging 24 families were found to be cold responsive.Notablely,the largest gene family was the AP2/ERF gene family followed by MYB and NAC.Taken together,these results give us a better understanding of cold-adaptive mechanism in this excellent cold-tolerant peach species.And the unique DEGs identified in this study provides useful information for further study on cold response mechanisms and genetic improvement of cold-resistance in Prunus persica. |
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