ABA signaling mediates 5-aminolevulinic acid-induced anthocyanin biosynthesis in red pear fruits

Peel color is an important quality trait of pears and directly affects its commercial value. Although several studies have reported that exogenous 5-aminolevulinic acid (ALA) induces anthocyanin biosynthesis, the mechanisms involved remain unclear. The purpose of this study was to confirm the effects of ALA on anthocyanin biosynthesis in the red pear 'Nanhong' and elucidate the effect of abscisic acid (ABA) on ALA-induced anthocyanin accumulation. Application of ALA solution (100 or 300 mg L-1) promoted arbutin, flavonol, and anthocyanin accumulation, but decreased chlorogenic acid and flavanol content, especially at 300 mg L-1. The structural gene transcriptional levels and transcription factors (PuMYB10 and PubHLH33) associated with anthocyanin synthesis were also enhanced by ALA treatment. Furthermore, ALA treatment increased the endogenous ABA content and upregulated the expression of ABA biosynthesis-related genes. Additionally, the influence of ALA on anthocyanin biosynthesis was removed by the ABA biosynthesis inhibitor fluridone, while the expression of PuMYB10, PuUFGT, and PuGSTF12, which were induced by exogenous ABA and ALA treatments, was suppressed. These results suggest that ABA signaling plays a crucial role in ALA-induced anthocyanin accumulation in red pear fruits. The results can provide a theoretical basis for improving the color and fruit quality of red pears.