The Abscisic Acid Regulation Mechanism Of Wild Strawberry In Response To Various Abiotic Stresses

Cultivated strawberries(Fragaria × ananassa)are delicious and nutritious.They are widely cultivated around the world and have extremely high economic and commercial values.As global climate change intensifies,the frequency of extreme weather increases.Abiotic stresses,including high temperature,low temperature,and drought have more and more serious effects on crop growth and yield.As the relative species of cultivated strawberry,wild strawberry has stronger tolerance to stress than cultivated strawberry.Therefore,research on the stress tolerance mechanism of wild strawberries will helpful for the cultivation of the cultivated strawberries with stronger stress tolerance.In this study,the tolerance of 5 diploid wild strawberries,including F.nilgerrensis,F.vesca,F.nubicola,F.daltoniana,and F.pentaphylla to heat,cold and drought stress were determined.The integrated transcriptomics and metabolomics methods were used to analyze the abscisic acid(ABA)regulation mechanism of wild strawberries with different tolerant abilities in response to heat,cold and drought stress.The main results of this study are as follows.(1)The low-temperature semi-lethal temperatures of F.nubicola,F.vesca,F.daltoniana,F.pentaphylla,F.nilgerrensis were-10.44℃,-8.90℃,-11.14℃,-9.29℃,-10.47℃,respectively,indicating that F.daltoniana had the strongest cold tolerance,while F.vesca had the weakest cold tolerance.The high temperature semi-lethal temperatures of F.nubicola,F.vesca,F.daltoniana,F.pentaphylla,F.nilgerrensis were 52.90℃,46.80℃,53.50℃,54.25℃ and 53.70℃,respectively,indicating that F.pentaphylla had the strongest heat tolerance,while F.vesca had the weakest heat tolerance.After treatment with 15%PEG-6000 for 6 days,the average membership function values of drought resistance indexes of F.nubicola,F.vesca,F.daltoniana,F.pentaphylla,F.nilgerrensis were 5.87,100.00,41.05,44.68,59.04,respectively,indicating that F.vesca had the strongest drought tolerance,while F.nubicola had the weakest drought tolerance.(2)Compared to untreated F.vesca and F.daltoniana,F.vesca and F.daltoniana under low temperature stress(-5℃)could increase the ABA content by up-regulating the ABA biosynthesis pathway gene NCED(LOC101315210)and down-regulating the expression of the ABA decomposition gene CYP707A(LOC101299092).WGCNA analysis revealed that ABA could regulate the expression levels of the amino acid metabolism pathway related genes in F.vesca under low temperature stress,resulting in a significant increase in glucose and fructose content.Under low temperature stress,ABA could regulate the expression of the starch and sucrose metabolism pathways and amino acid metabolism pathways related genes in F.daltoniana resulting in a significant increase in glucose and fructose content.These results indicated that the accumulation of glucose and fructose could play an important role in the cold-tolerance of strawberries,and reduce the damage of F.vesca and F.daltoniana under low temperature stress.12 transcription factors played a role in the ABA regulatory mechanism and some genes that may be related to the accumulation of glucose and fructose.Compared with F.vesca leave,F.daltoniana leave had more ABA accumulation,so that F.daltoniana can regulates lowtemperature response genes more significantly than F.vesca by ABA,which might be the main mechanism of the stronger cold tolerance of F.daltoniana than F.vesca.Under low temperature stress,ABF2(LOC101302803)was significantly up-regulated in the leave of F.daltoniana and down-regulated in F.vesca,which may make F.daltoniana has stronger glucose signal transduction ability.This may be the reason why F.daltoniana leaves had the higher activity of ROS scavenging enzyme POD and the lower damage to the cell membrane of strawberry leave with F.daltoniana than F.vesca under low temperature stress,which made F.daltoniana have a stronger cold tolerance.(3)Compared to untreated F.vesca and F.pentaphylla,F.vesca and F.pentaphylla could increase the expression of ABA biosynthesis pathway gene NCED(LOC101315210)under high temperature stress(42℃),which makes ABA accumulation increase significantly.PYL(LOC101296751,LOC101297328,LOC101308767)and SnRK2(LOC101300148,LOC101300914,LOC101301056,LOC 101304512,LOC101307307)may be the key genes for ABA signal transduction in wild strawberry under high temperature stress.WGCNA analysis revealed that ABA could regulate the expression of genes in the pentose phosphate pathway and amino acid biosynthesis pathway in wild strawberry under high temperature stress,which made proline and other amino acid metabolites increase significantly.These restults indicated that the accumulation of amino acids such as proline could play an important role in the heat-tolerance mechanism of wild strawberries,and reduce the damage of wild strawberries under high temperature stress.21 transcription factors played a role in the ABA regulatory mechanism and some genes that may be related to amino acid accumulation.Compared with F.vesca leave,F.pentaphylla leave had more ABA accumulation,and the up-regulation of ABF4(LOC101291997)gene expression in F.pentaphylla leave may increase its ABA sensitivity under treatment of high temperature stress for 12h,so that the F.pentaphylla can regulate high temperature response genes through ABA more significantly than F.vesca,which might be the main mechanism of the stronger heat tolerance of F.pentaphylla than F.vesca,This might be the reason why F.pentaphylla leave had higher activity of ROS scavenging enzyme POD,and the degree of cell membrane damage and membrane lipid peroxidation were lower than F.vesca leave under high temperature stress,which made F.pentaphylla have a stronger heat resistance.(4)Compared to untreated F.vesca and F.nubicola,F.vesca and F.nubicola could increase the accumulation of ABA by up-regulating the ABA biosynthesis pathway gene NCED(LOC101311757)and down-regulating the expression of the ABA decomposition gene CYP707A(LOC101294153)under simulated drought stress(20%PEG-6000).PYL(LOC101297328,LOC101295297)could be the key gene of ABA signal transduction in wild strawberry under drought stress.WGCNA analysis revealed that ABA could regulate the fructose and mannose metabolism and amino acid biosynthesis pathway genes under drought stress,which increased the accumulation of carbohydrates and amino acids,and reduced the damage of wild strawberries under drought stress.10 transcription factors played a role in the ABA regulatory mechanism and some genes that may be related to amino acid accumulation.The main mechanism for the strong drought tolerance of F.vesca may be that,compared with the leave of untreated F.vesca and F.nubicola,the fructose and mannose metabolism pathway genes ALDO(LOC101300606)and GMPP(LOC101301200)were significantly down-regulated in F.vesca leave and significantly up-regulated in F.nubicola leave under simulates drought stress,which made the sugar content significantly increased in F.vesca leave,but no significant change in F.nubicola leaves.Under 20%PEG-6000 simulated drought stress,the content of proline,glucose and fructose increased significantly in F.vesca,but not significantly changed in F.nubicola,which may be the main reason why F.vesca had the stronger drought tolerance than F.nubicola.In summary,under the stress of high temperature,low temperature and drought,wild strawberries may regulate the expression of transcription factors through ABA,thereby regulating sugar metabolism and amino acid metabolism to reduce the damage.The research results provide a theoretical basis for cultivating cultivated heat-tolerant,cold-tolerant or drought-tolerant strawberries.