Functional Analysis Of Apple Small G Protein MdRabE1b In Response To Salt And N-deficient Stress In Malus

As an excellent apple producing area in China,Loess plateau region is limited by low precipitation,large evaporation and soil salinization,and salt and low nitrogen stress are two important adversity problems faced by apple industry in this region.Rab protein is involved in regulating tolerance of various stresses.Current studies suggest that Rab GTPase protein is involved in autophagy pathway in yeast and animal cells.The lab early had explicit the autophagy in response to low nitrogen stress and salt stress,the experiment with small apple G protein MdRabE1b as the object,using apple transgenic technology for genetically modified,was studied by physiological and metabolic analysis systematically autophagy genes involved in apple’s response to salt stress and low nitrogen stress function and may participate in regulating autophagy pathway.The main research results are as follows.1.Under salt stress,the content of MDA in leaves of transgenic plants（OE）was about 1.4 times that of wild type（WT）,while the relative electrical conductivity of transgenic plants was about 1.5 times that of WT.The cell membrane system of OE was more seriously damaged.The decrease of net photosynthetic rate of OE was about 1.3 times of that of WT.The stomatal aperture,chlorophyll content and Fv/Fm of OE were lower than that of WT,and the photosynthetic system of OE was more severely damaged,resulting in the decrease of relative growth rate and net biomass of OE much higher than that of WT.Moreover,the contents of H₂O₂ and O₂^-in leaves of OE were higher than those of WT,and the activities of antioxidant enzymes were also lower than those of WT.The expression levels of MdSOS1,MdSSOS2,MdSOS3,MdHKT1,MdNHX1 and MdAKT1 were both up-regulated by salt stress,and the expression levels in OE were lower than that in WT.After 15 days of salt stress,the expression of autophagy genes in OE was significantly lower than that of WT.The cell membrane system of transgenic plants was more seriously damaged.2.Under low nitrogen stress,the net photosynthetic rate of OE decreased 1.2 times as much as that of WT,stomatal conductivity,net transpiration rate,total chlorophyll content,stomatal aperture and Fv/Fm of OE were all lower than those of WT.The relative growth rate and net biomass of OE were significantly lower than that of WT,and the root growth of OE was worse than that of WT.In this study,after low N stress,the gene expression levels of AMT family and NRT family in OE were lower than those in WT,and the NUE and nitrogen absorption flux of OE were also significantly lower than those in WT.In addition,the activities of nitrogen metabolizing enzymes in OE were lower than those in WT,and correspondingly,the nitrogen use efficiency of OE was lower.After 30 days of low nitrogen treatment,the autophagy activity analysis showed that the expression levels of autophagy-related genes and the number of autophagosomes in the roots of OE were lower than that of the WT.These results indicated that overexpression of MdRabE1b weakened the tolerance of apple plants to low nitrogen stress.