Integrated multi-omics analysis to elucidate the role of shikimic acid and phenethylamine in the effect of scions on rootstocks of Camellia oleifera

Camellia oleifera is an important industrial crop whose leaf, flower, pericarp, and seed have multiple application values. Grafting is the main means of C. oleifera propagation, and the quality of grafted seedlings is directly related to the propagation coefficient and yield promotion. However, the research on C. oleifera grafting is lacking, and there is little comprehensive understanding of the growth characteristics, metabolic patterns, and molecular mechanisms of different grafting combinations of C. oleifera. In this study, the phenotypic, metabolomic, and transcriptomic profiles of four grafting combinations [C. oleifera (Co), C. yuhsienensis (Cy), C. chekiangoleosa (Cc), and C. gigantocarpa (Cg) four kinds of scions grafted onto one rootstock, C. oleifera (Co)] were investigated. The phenotypic analysis showed that hetero-grafting inhibited the growth vigor of grafted unions. The abundance of shikimic acid and phenylethylamine in hetero-grafting was lower than in auto-grafting based on the differential metabolite analysis, and the exogenous addition of both metabolites promoted the growth of grafted unions. Multi-omics analysis revealed that hetero-grafting could significantly affect the differential expression of hub genes (aroD, aroE, aroK, pheA, tyrB) in the biosynthesis of shikimic acid and phenylethylamine and that AP2/ERF, MYB, and GRAS transcription factors were involved in regulating the expression of the above hub genes. These findings innovatively characterized the important role of shikimic acid and phenethylamine in the growth of C. oleifera grafted seedlings and provided new insights for promoting the propagation and industry development of C. oleifera.