Function Analysis Of Apple Sucrose Nonfermenting-1-Related Kinase Gene MpSnRK2.10 Under Salt Stress

Apple(Malus domestica)is one of the most important fruit tree species in the world,and its growth and development are severely restricted by unfavorable environmental factors such as frequent drought,salinity and freezing damage in the Loess Plateau of Northwest China.TheSnRK2 subfamily of sucrose non-fermentation-related protein kinases is one of the plant-specific serine/threonine protein kinases.In this experiment,apple sucrose nonfermenting-1-related kinase genes MpSnRK2.10 was used as the research object,and the MpSnRK2.10-overexpressing transgenic apple line obtained earlier was used to systematically study the function of MpSnRK2.10 in regulating apple response to salt stress by ABA signaling pathway.The main findings are as follows:1.Using the transgenic apple seedlings overexpressing MpSnRK2.10 as the test material,the effect of MpSnRK2.10 in regulating apple’s response to salt stress was studied by hydroponic experiments.The results showed that the expression of MpSnRK2.10 was induced by salt stress,and overexpression of MpSnRK2.10 could significantly alleviate the effect of salt stress on the growth of apple plants.The relative conductivity,malondialdehyde and reactive oxygen species levels of overexpression plants were lower;chlorophyll content,SOD activity,photosynthetic capacity and accumulation of several amino acids were higher than those of wild type plants;Na~+accumulation in overexpression plants was less under salt stress and the expression levels of several genes Md HKT1,Md AKT1,Md NHX2,Md NHX4,Md SOS1 and Md SOS2 involved in ion balance under salt stress were up-regulated.In addition,this study found that the ABA content and stomatal pore size of the overexpressed plants were larger than those of the wild-type plants under salt stress,and ABA-related genes(Md NCED4-4,Md AREB1.1,Md AREB1.2,Md AREB3.2,Md ABF3-1,Md ABF3-2)was higher,while the expression levels of ABA catabolism genes(Md CYP707A1 and Md CYP707A2)were significantly lower than those in wild-type plants.The above results indicated that overexpression of MpSnRK2.10 improved the tolerance of apple plants to salt stress.2.Using overexpressing MpSnRK2.10 transgenic apple seedlings as test materials,the relationship between MpSnRK2.10 regulating apple’s response to salt stress and ABA signaling pathway was studied by exogenously adding ABA and its inhibitor.The results showed that:under salt stress,the physiological state of plants was changed when tissue culture seedlings were treated with exogenous ABA and ABA inhibitor nordihydroguaiaretic acid(NDGA)for 10 days.The application of NDGA significantly narrowed the phenotypic differences between wild-type and overexpressing plants,with the most obvious changes in relative conductivity and chlorophyll content.At the same time,potted seedlings were used as test materials for salt stress treatment,and ABA and its inhibitors were applied externally.The results showed that only ABA treatment had no obvious effect on the phenotype of apple plants under salt stress,and exogenous ABA alleviated the apple plants of each line.The phenotypic difference between the overexpressed and wild-type plants was reduced by exogenous application of NDGA,and there was no significant difference in relative conductivity,MDA content,photosynthetic capacity and antioxidant capacity between the two plants under salt stress.In addition,after NDGA treatment,the stomatal opening of the overexpressing plants was equal to that of the wild-type gene,and the level of endogenous ABA was similar.The difference in expression levels of some genes(Md DREB2,Md DREB3,Md EPF1,Md EPF2,Md EPFL5,Md NCED1-1,Md NCED4-2,Md NCED4-3,Md NCED4-5)related to ABA signaling pathway was reduced between overexpressed and wild-type plants.Further research found that some amino acids(Phe,Met,Arg,Gly,His,Thr)were induced to accumulate more in overexpressed plants under salt stress,while exogenous NDGA inhibited their excessive accumulation in overexpressed plants.The above results indicated that when the ABA pathway was inhibited,the ability of overexpressing plants to resist salt stress decreased,which indicated that MpSnRK2.10 was dependent on the ABA signaling pathway to regulate apple response to salt stress.