Apple Scion Cultivars Regulate Root-Rhizobacteria Crosstalk Through Photosynthetic Product-Mediated Sugar Metabolism

In grafted combinations, the scion cultivar, representing the aboveground portion, possesses the potential to influence the rhizosphere bacterial community. However, the precise mechanisms by how the scion cultivar contributes to the recruitment and assembly of rhizosphere bacteria remain poorly understood. In this study, we conducted a comprehensive analysis of the root transcriptome and metabolomics coupled with the amplification of the rhizosphere bacterial 16S rRNA gene. We found that scion cultivars with different net photosynthesis rates significantly impacted root metabolites and the expression of root sugar metabolism genes. Moreover, rhizosphere-specific taxa (Rhizobium, Nitrospira and Ensifer) are associated with root sugar metabolites, particularly sucrose. The foliar application of 2% sucrose on leaves enhanced root sugar metabolism and shaped the rhizosphere microbiota, notably promoting the growth and colonization of the bacterial isolation in the rhizosphere of apple plantlets. This study has significant implications for future studies on plant-microbe interactions in grafted combinations.