Functional Identification of ANR Gene in Apple (Malus halliana) Demonstrates It Reduces Saline-alkali Stress Tolerance.

Abstract

As one of the major abiotic stresses restricting the development of global agriculture, saline-alkali stress can cause osmotic stress, ion poisoning, reactive oxygen species damage and high pH value damage, which seriously restricts the sustainable development of fruit industry. Therefore, it is of great significance to cultivate saline-alkali resistant apple rootstocks to improve the yield and quality of apple in China. Based on transcriptome data, MhANR (LOC114827797), which was significantly induced by saline-alkali stress, was cloned from Malus halliana. The physicochemical properties, evolutionary relationships and cis-acting elements were analyzed. Subsequently, the tolerance of MhANR overexpression in Arabidopsis thaliana, tobacco and apple calli to saline-alkali stress was verified by genetic transformation. Transgenic plants presented lower chla, chlb and proline contents, lower Superoxide dismutase (SOD), Peroxidase enzyme (POD) and Catalase enzyme (CAT) activities, and higher relative electrical conductivity (REC) compared to those in WT plants under saline-alkali stress. In addition, the expression levels of saline-alkali stress related genes in overexpressed apple calli also diaplayed lower values compared to WT calli, including antioxidant genes MhSOD and MhCAT, Na+ transporter genes MhCAX5, MhCAX5, MhSOS1, MhALT1, and H+ -ATPase genes MhAHA2 and MhAHA8, while the expression levels of K+ transporter genes MhSKOR and MhNHX4 displayed higher values. In conclusion, MhANR reduced the tolerance of Arabidopsis thaliana, tobacco and apple calli under saline-alkali stress by regulating osmoregulatory substances, Chlorophyll content, antioxidant enzyme activity and expression of saline-alkali stress-related genes, which provided a theoretical basis for cultivating apple rootstocks with effective saline-alkali stress tolerance.