Grafting enhances growth vigor and photosynthetic capacity in the progeny of critically endangered Abies beshanzuensis

Abies beshanzuensis is a critically endangered conifer species in the Pinaceae family, with only three wild adult trees (progenitor trees) remaining in its native habitat. To conserve its germplasm, A. beshanzuensis scions were grafted onto A. firma rootstocks, which significantly improved the growth and reproduction of the grafted plants. However, the effects of grafting on the growth and development of progeny of grafted A. beshanzuensis, as well as the underlying mechanisms, remain unclear. In this study, we compared seedling-stage growth differences between progeny of progenitor trees (PP) and grafted trees (GP), revealing significantly greater plant height and stem diameter in GP. Physiological analysis of leaf tissues showed significantly higher auxin levels in GP, increased chlorophyll content and enhanced maximum photochemical efficiency (Fv/Fm) compared to PP. De novo transcriptome assembly using PacBio and Illumina RNA-Seq identified 2,638 differentially expressed genes (DEG) between PP and GP, with significant changes in genes involved in auxin signaling and chlorophyll biosynthesis pathways in GP. Methylation-sensitive amplified polymorphism (MSAP) analysis further revealed a lower average DNA methylation level in GP compared to PP. We propose that grafting reduces DNA methylation-mediated repression of genes involved in the auxin signaling and chlorophyll synthesis, thereby enhancing seedling vigor and photosynthetic capacity. These findings provide a theoretical foundation and novel insights for the conservation of endangered woody plants, with broader implications for biodiversity preservation in the context of global climate change.