The eTM-miR858-MYB62-like module regulates anthocyanin biosynthesis under low-nitrogen conditions in Malus spectabilis.

The anthocyanin content increases in Malus spectabilis leaves under low-nitrogen conditions. Noncoding RNAs are indicated to play key regulatory roles in anthocyanin biosynthesis. However, the functional roles of noncoding RNAs in anthocyanin biosynthesis under low-nitrogen conditions remain elusive. In this study, miR858 was screened as a key regulator of anthocyanin biosynthesis under low-nitrogen conditions through whole-transcriptome sequencing. Then we used miR858 as an entry point to explore the regulatory network of lncRNA-miRNA-mRNA by dual-luciferase reporter assays and GUS histochemical staining assays, as well as to identify the mechanism of this regulatory network in anthocyanin biosynthesis by both transient and stable transformation experiments in Malus. MiR858 overexpression increased total anthocyanin content. MiR858 acted by negatively regulating its target gene, MsMYB62-like, under the low-nitrogen condition. MsMYB62-like inhibited the expression of MsF3'H, thereby negatively regulating anthocyanin biosynthesis. In addition, eTM858-1 and eTM858-2 were identified as endogenous target mimics of miR858 that bind to miR858 to prevent cleavage of MsMYB62-like and thereby negatively regulate anthocyanin biosynthesis. The results clarify the mechanism through which the eTM-miR858-MYB62-like module regulates anthocyanin biosynthesis in Malus under low-nitrogen conditions.