Functional identification of ANR genes in apple ( Malus halliana ) that reduce saline–alkali stress tolerance

As one of the major abiotic stresses restricting the development of global agriculture, saline–alkali stress causes osmotic stress, ion poisoning, ROS damage and high pH damage, which seriously restrict sustainable development of fruit industry. Therefore, it is essential to develop and cultivate saline–alkali‐resistant apple rootstocks to improve the yield and quality of apples in China. Based on transcriptome data, MhANR (LOC114827797), which is significantly induced by saline–alkali stress, was cloned from Malus halliana . The physicochemical properties, evolutionary relationships and cis ‐acting elements were analysed. Subsequently, the tolerance of MhANR overexpression in Arabidopsis thaliana , tobacco, and apple calli to saline–alkali stress was verified through genetic transformation. Transgenic plants contained less Chl a , Chl b and proline, SOD, POD and CAT activity, and higher relative electrical conductivity (REC) compared to WT plants under saline–alkali stress. In addition, expression of saline–alkali stress‐related genes in overexpressed apple calli were also lower than in WT calli, including the antioxidant genes ( MhSOD and MhCAT ^), the Na + transporter genes ( MhCAX5 , MhCAX5 , MhSOS1 , MhALT1 ), and the H + ‐ATPase genes ( MhAHA2 and MhAHA8 ), while expression of the K + transporter genes ( MhSKOR and MhNHX4 ) were higher. Expression of MhANR reduced tolerance of A. thaliana , tobacco, and apple calli to saline–alkali stress by regulating osmoregulatory substances, chlorophyll content, antioxidant enzyme activity, and expression of saline–alkali stress‐related genes. This research provides a theoretical basis for cultivating apple rootstocks with effective saline–alkali stress tolerance.