Characterization Of MdPIP2;2,a Target Of MdSUMO2A,in Response To Drought Stress In Apple

Apple is one of the most popular fruits in the world.Northwest loess plateau region is the best apple producing area in China.However,because it is located in the semiarid and arid area,rainfall is annually less and unevenly distributed,which hinders development of apple industry in this region.Plasma membrane intrinsic protein PIPs(plasma membrane intrinsic proteins),a subfamily of water channel protein(Aquaporins,AQPs),is localized on the cytoplasmic membrane.PIPs can selectively transport water and other small neutral molecules across cytoplasmic membrane efficiently,resulting in its involvement in the processes of absorption and transportation of water in plant.In this thesis,MdPIP2;2 gene was cloned from the Golden Delicious apple.Tissue specific expression and expression patterns in response to drought,high temperature,low temperature stress,and ABA treatment of MdPIP2;2 were studied.By using SUMOylation system constructed in Escherichia coli,we verified that MdPIP2;2 is the target of MdSUMO2 A.The function of MdPIP2;2 gene under drought and high temperature stress was characterized by using MdPIP2.2 OE transgenic plants.The main results obtained are as follows:1.Cloning and analysis of MdPIP2;2 gene in apple.MdPIP2;2 gene was cloned from apple.The CDS region of MdPIP2;2 is 846 bp,encoding 281 amino acids in total.The analysis of MdPIP2;2 gene showed that MdPIP2;2 gene was expressed in root,stem,leaf,flower and fruit of apple,and the expression level in flower was the highest.After drought,high temperature stress and ABA treatment,the expression of MdPIP2;2 gene was decreased gradually,indicating that MdPIP2;2 gene is responsive to drought,high temperature and ABA.2.MdPIP2;2 can be SUMOylated and the SUMOylation site was the lysine 272 of MdPIP2;2.Among the three SUMO proteins in apple genome(MdSUMO2A,MdSUMO2 B and MdSUMO2C),only MdSUMO2 A has the function to SUMOylate MdPIP2;2.3.Compared with non-transgenic plants GL-3,MdPIP2;2 OE transgenic plants were more sensitive to drought stress.MdPIP2;2 OE transgenic plants showed more serious wilting degree,and lower relative water content in leaves,and lower photosynthetic rate and survival rate after short-term drought treatment.4.MdPIP2;2 negatively regulated apple drought resistance by adjusting stomatal opening and closing.After exogenous ABA treatment,MdPIP2;2 OE transgenic plants were insensitive to ABA and the stomatal closure degree of MdPIP2;2 OE transgenic plants was much lower than that of GL-3.