苹果是我国第一大水果，而盐胁迫是影响苹果产业的重要非生物胁迫。我们知道，苹果碳营养水平的高低对于树体适应外界非生物胁迫起重要的作用，但具体机理尚不清楚。申请人前期研究发现，影响苹果碳营养水平的MdHXK1（己糖激酶）基因表达受盐胁迫诱导。MdHXK1转基因愈伤抗盐性分析表明， MdHXK1正调控苹果愈伤抗盐性。采用免疫共沉淀质谱鉴定筛选到Na+/H+逆向转运蛋白MdNHX1，推测MdHXK1可能与MdNHX1互作调控苹果植株抗盐性。为证实该设想，本研究拟利用酵母双杂及Pull-down等技术进一步证明两者互作。同时，磷酸化检测MdHXK1对MdNHX1蛋白稳定性及Na+/H+转运活性的调控。最后，一系列转基因分析证明MdHXK1通过MdNHX1提高苹果植株抗盐能力。本研究预从分子水平阐明MdHXK1提高苹果抗盐性的机理，对筛选和培育抗盐性强的苹果品种具有指导意义。

Apple (Malus domestica Borth.) is one of the most economically important fruit crops worldwide, however, the production and quality of apple fruits severely affected by secondary soil salinization. As is well known, carbon nutrition level plays an important roles in defensing various abiotic stresses such as salt stress in apple, but the exact mechanism is poorly understood. In our preliminary studies, qRT-PCR assay was used and found that the expression of MdHXK1, a hexokinase which influences carbon nutrition level in apple, was induced by salt stress. Salt tolerance assays showed that overexpression of apple MdHXK1 in apple calli enhanced the resistance to salt stress. In addition, Co-IP screen assays demonstrated that MdNHX1, an apple Na+/H+ antiporter in the tonoplast, possibly also involved in MdHXK1-mediated increase of salt tolerance. To verify this hypothesis, yeast-two hybrid and pull-down assays was used to confirm that MdHXK1 physically interacts with MdNHX1. Meanwhile, in vitro kinase assay was performed to determine the stabilization of MdNHX1 protein and Na+/H+ transport activity by MdHXK1 protein kinase. Finally, a series of transgenic analyses in apple plants and ‘Orin’ apple calli demonstrated that MdHXK1 increased the resistance of salt stress in a MdNHX1-dependent manner. In summary, our findings would provide new insights into the mechanism by which MdHXK1 increases salt tolerance by regulating MdNHX1, and have an important guiding significance in screening and creating salt-tolerant apple varieties in the future.