MdFC2, a ferrochelatase gene, is a positive regulator of ALA-induced anthocyanin accumulation in apples

5-Aminolevulinic acid (ALA), a key biosynthetic precursor of tetrapyrrole compounds, significantly induces anthocyanin accumulation in apple (Malus × domestica Borkh.) as well as other fruits. Although the molecular mechanisms of ALA-induced anthocyanin accumulation have been reported, it remains unknown whether the metabolism of ALA is involved in ALA-induced anthocyanin accumulation. Here, we found that MdFC2, a gene encoding ferrochelatase (MdFC2), which catalyzes the generation of heme from protoporphyrin lX (PPIX), may play an important role in ALA-induced apple anthocyanin accumulation. Exogenous ALA induced the MdFC2 expression as well as anthocyanin accumulation in apple leaves, calli, and isolated fruits. MdFC2 overexpression in apple leaves or calli significantly enhanced anthocyanin accumulation as well as the expression of genes involved in anthocyanin biosynthesis, while RNA interference MdFC2 inhibited anthocyanin accumulation and the expression of genes involved in anthocyanin biosynthesis. When 2,2'-dithiodipyridine, an inhibitor of MdFC2, was added, ALA-induced anthocyanin accumulation was blocked. These results suggest that ALA-induced anthocyanin accumulation of apple may be regulated by heme or its biosynthesis, among which MdFC2 or MdFC2 may play a critical positive regulatory role. This finding provides a novel insight to explore the mechanisms of ALA-regulating physiological processes and better application of ALA in high-quality fruit production.