Transcriptome and hormonal analysis of grafting process by investigating the homeostasis of a series of metabolic pathways in Torreya grandis cv. Merrillii

Grafting greatly reduces the juvenile phase length and makes the large-scale cultivation of Torreya grandis possible. Genomic information for the Torreya genus is not yet available. This study aimed at exploring the regulation mechanisms underlying the grafting process. Samples harvested from the rootstock and scion (0.5 cm from the junction) of T. grandis were used for high-throughput sequencing. The differentially expressed genes (DEGs) belonging to metabolisms were investigated, and 39 metabolic pathways were found to be significantly enriched during the grafting process. These metabolic pathways included several flavonoid biosynthesis and metabolism-related pathways, suggesting that the amount of antioxidant secondary metabolites may play an essential role in the grafting process of T. grandis. Many DEGs encoding various hormone-signaling components were also identified and so the graft process in T. grandis may be controlled by an intricate hormonal signaling network. The expression pattern of auxin response factors under different conditions during the graft process were also investigated. Furthermore, data showed that 1-N-naphthylphthalamic acid treatment inhibited the accumulation of auxin in both the rootstock and scion and affected the homeostasis of a series of metabolic pathways during the grafting process in T. grandis. Auxin and auxin transport may participate in the regulation of the grafting process by affecting the activities of numerous metabolic pathways.