Functional identifification of LAR genes in apple (Malus halliana) demonstrates that it enhances saline-alkali stress tolerance

The impact of soil salinization on the production and development of fruit trees is becoming increasingly serious and has become a major environmental problem worldwide. Plants have evolved a series of elaborate defense systems in response to saline-alkali stress. Proanthocyanidins contain powerful antioxidant properties, due to being a peroxidation inhibitor and oxygen free radical scavenger. LAR is a key gene in procyanidin synthesis. It has been much less addressed whether LAR participates the response to saline-alkali stress. The physicochemical properties, evolutionary relationships and cis-acting elements of LAR genes were analyzed. It was found that MhLAR was closely related to Pyrusxbretschneideri, and its promoter region was present in stress-related regulatory elements, suggesting that MhLAR might be involved in abiotic stress. In addition, the tolerance of MhLAR overexpression in Arabidopsis thaliana, tobacco, and apple calli to saline-alkali stress was verified through genetic transformation. Compared with the wild type, transgenic plants grew better under saline-alkali stress, the contents of chlorophyll, proanthocyanidin and proline were increased by 75.35%, 93.55% and 51.15%, respectively. The activities of antioxidant enzymes Superoxide Dismutase (SOD), Peroxisome (POD) and Catalase (CAT) were increased. The Relative conductivity (REC) and Malondialdehyde (MAD) content were reduced by 11.32% and 20.15%. These results indicate that MhLAR can respond to saline-alkali stress and play a positive regulation role.