MdNAC2 enhances K⁺ deficiency stress tolerance by maintaining K⁺ homeostasis in apple

Potassium (K) is an essential nutrient for apple production, with its deficiency severely compromising yield and fruit quality. The development of K deficiency-resistant rootstocks represents an effective and promising approach to alleviating the adverse effects of K deficiency stress. However, the molecular mechanisms underlying apple resistance to K deficiency remain poorly understood. Here, we identified the transcription factor MdNAC2 as a critical regulator of apple tolerance to K deficiency through RNA-seq using Malus hupehensis as material. MdNAC2 enhanced apple tolerance to K deficiency by maintaining K⁺ homeostasis, primarily through directly suppressing the expression of the K⁺ efflux transporter MdGORK1. This regulatory mechanism reduces K⁺ efflux and stabilizes intracellular K⁺ levels under K deficiency stress. Collectively, our findings highlight the pivotal role of the MdNAC2-MdGORK1-K⁺ regulatory module in maintaining K⁺ and conferring apple resistance to K deficiency. This study provides new insights into the molecular mechanisms of K deficiency tolerance and establishes a theoretical foundation for breeding K deficiency-resistant apple rootstocks and cultivars.