Nitrate is the major nitrogen source for higher plants. In addition to serving as a nutrient, it is also a signaling molecule that regulates plant growth and development. Although membrane-bound nitrate transporter/peptide transporters (NRT/PTRs) have been extensively studied and shown to regulate nitrate uptake and movement, little is known about how these factors are regulated by the external nitrogen environment. Red-fleshed apple, whose coloration is determined by the transcription factor MdMYB10, had higher nitrate uptake efficiency than non-red-fleshed apple. Nitrate assimilation and utilization were higher in red-fleshed apple cultivars, and comparative transcriptome analysis showed that the expression of genes encoding the NRT2s was increased in red-fleshed apple. In vitro and in vivo experiments showed that MdMYB10 directly bound to the MdNRT2.4-1 promoter to transcriptionally activate its expression, resulting in enhanced nitrate uptake. MdMYB10 also controlled nitrate reallocation from old leaves to new leaves through MdNRT2.4-1. Overall, our findings provide novel insights into the mechanism by which MdMYB10 controls nitrate uptake and reallocation in apple, which facilitates adaptation to a low-nitrogen environment.

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