Transcriptomic analyses reveal the effects of grafting on anthocyanin biosynthesis in crabapple

Anthocyanins are crucial plant pigments that enhance plant color and bolster resistance. Grafting is an ancient cultivation technology in Malus production, and it has important effects on plant phenotypes, secondary metabolism, biotic, and abiotic resistance. However, the underlying genetic and regulatory mechanisms effects on anthocyanin biosynthesis are unclear. In this research, the phenotypic and transcriptome variation in Malus crabapple cv.'Indian Magic' (Spring-red-leaf) and Malus Crabapple cv.'Flame' (evergreen leaf) serving as either rootstockor scion (F/I, I/F) and self-grafted (I/I) as control were explored. The results showed that the anthocyanin accumulation in the stem of 'Flame' grafted onto 'Indian Magic' occurred rather than being induced by wounding and other stresses. Based on KEGG analyses, it was deduced that the anthocyanin accumulation is mainly induced by 'plant hormone signal transduction', 'starch and sucrose metabolism', and the 'MAPK signaling pathway'. Moreover, transcriptomic analyses also revealed MdSAUR20 was highly induced during grafting, potentially playing a pivotal role in grafting- induced anthocyanin accumulation, as confirmed by transgenic assay. These results propose new insight into regulating anthocyanin biosynthesis and contributing signal transport in grafting, contributing to a better understanding of the selection and combination of scion and rootstock in the grafting process.