The Function And Mechanism Of An Apple Cytoplasmic Malate Dehydrogenase Gene In Regulating Abiotic Stress Tolerance

Up to now, the function and mechanism of cyMDH are still absent. In this study, the apple MdcyMDH gene was cloned and the MdcyMDH-overexpressed lines were obtained. Additionally, the impacts of MdcyMDH overexpression on growth and abiotic stress tolerance were evaluated, and the mechanism underlying stress tolerance was investigated. The primary results are as follows:1. The apple MdcyMDH and its isoforms were isolated and their expression in different tissues and in responses to cold and salt stresses was conducted. The results showed that there are five cyMDH isoforms in apple genome, which were constitutively expressed in different tissues; MdcyMDH, MDP0000174740 and MDP0000197620 were primarily expressed in stem and root; MdcyMDH, MDP0000174740 and MDP0000170418 were transcriptionally induced by cold and salt; MdcyMDH and MDP0000174740 might poccess the similar function based on their expression patterns.2. The two MdcyMDH-overexpressed lines 5 and 7 were obtained by kanamycin and PCR screening.3. The influences of MdcyMDH-overexpression on growth were investigated. The results showed that MdcyMDH-overexpression led to insignificantly enhanced above-ground height and total weight and significantly increased total root weight.4. The evaluation of abiotic stress tolerance indicated that MdcyMDH-overexpression improved the tolerances of the transgenic plants to cold and salt stresses in comparsion to the control plants.5. A digital gene expression tag profiling analysis revealed that MdcyMDH overexpression largely altered some biological processes, including hormone signal transduction, photosynthesis, citrate cycle and oxidation–reduction. Further experiments verified that MdcyMDH overexpression modified the mitochondrial and chloroplast metabolisms and elevated the level of reducing power, primarily caused by increased ascorbate and glutathione, as well as the increased ratios of ascorbate/dehydroascorbate and glutathione/glutathione disulphide, under normal and especially stress conditions. Concurrently, the transgenic plants produced a high H₂O₂ content, but a low O2- production rate was observed compared to the WT plants. On the other hand, the transgenic plants accumulated more free and total salicylic acid?SA? than the WT plants under normal and stress conditions.