Nitrogen (N) and potassium (K) have significant effects on apple peel color. To further understand the molecular mechanism of N-K regulation of apple color, we analyzed the apple peel under different N and K treatments using isotope labeling, transcriptomics, and metabolomics. Under high N treatments, fruit red color and anthocyanin content decreased significantly. High N decreased the 13C distribution rate and increased the Ndff values of fruits, while K increased the expression of MdSUTs and MdSOTs and promoted 13C transportation to fruits. Anthocyanin-targeted metabonomics and transcriptome analysis revealed that high N downregulated the expression of structural genes related to the anthocyanin synthesis pathway (MdPAL, Md4CL, MdF3H, MdANS, and MdUFGT) and their regulators (MdMYBs and MdbHLHs), and also decreased some metabolites contents. K alleviated this inhibition and seven anthocyanins were regulated by N-K. Our results improve the understanding of the synergistic regulation of apple fruit coloring by N-K.
Keywords: anthocyanin; metabolomics; nitrogen; potassium; transcriptomics.