Engineering saline-alkali-tolerant apple rootstocks by overexpressing MdHYL1 in M9-T337.

Apple trees are frequently subjected to varying degrees of salt stress. HYL1, a key protein involved in miRNA biosynthesis, has been shown to play critical roles in plant responses to cold, drought, and pathogen infection. However, the specific function of MdHYL1 in mediating salt-alkali stress tolerance in apple remains unknown. In this study, we demonstrated that overexpression of MdHYL1 in M9-T337 rootstocks significantly enhanced salt-alkali stress tolerance, including improved growth performance, reduced Na⁺/K⁺ ratio, decreased membrane damage, enhanced photosynthetic, and antioxidant capacity, which significantly impairs their growth, fruit quality, and yield. Moreover, scions grafted onto MdHYL1 OE rootstocks displayed superior saline-alkali stress tolerance compared to those grafted onto M9-T337 rootstocks. Taken together, our findings highlight MdHYL1 as a promising candidate gene for improving saline-alkali stress tolerance in fruit trees through biotechnological approaches.

Supplementary information: The online version contains supplementary material available at 10.1007/s11032-025-01579-9.