Endophytic fungi enhance plant growth and stress resilience, yet their molecular roles in the roots of the endangered tree Phoebe bournei remain unclear. A comparative RNA-seq analysis was performed on root transcriptomes from wild, endophyte-colonized adult trees (OT) and axenically grown seedlings (ST). Unmapped reads were analyzed against the NCBI nucleotide (NT) database using BLASTN (v2.17.0), revealing Rhizophagus irregularis as the predominant endophytic fungus. Differential expression analysis identified 5891 DEGs, which were significantly enriched in pathways related to plant–pathogen interactions, phenylpropanoid biosynthesis, plant hormone signal transduction, and MAPK signaling. Key upregulated genes included PbMPK3, PbCML42, PbCML41.2, and PbGSTU28, suggesting enhanced ROS scavenging, calcium signaling, and defense activation. RT-qPCR validation confirmed the transcriptomic trends for selected genes. Our findings reveal that root endophytic fungi modulate a coordinated network involving immune priming, phytohormone regulation, and redox homeostasis, thereby supporting root development and enhancing resistance to biotic and abiotic stresses in P. bournei. This study provides foundational molecular insights into beneficial plant–endophyte interactions and identifies candidate genes that are valuable for the conservation and breeding of this threatened species.

Phoebe bournei, a rare tree species native to China, holds considerable economic importance. The heat shock protein 70 (Hsp70) family is a group of molecular chaperones that is broadly distributed across living organisms and play a critical role in processes like growth, development, and stress response. While Hsp70 genes have been identified and studied in various plant species, their specific functions in the growth and development of P. bournei remain unexplored. We performed a comprehensive analysis of the Hsp70 gene family in P. bournei, identifying a total of 45 Hsp70 genes, which were classified into four groups (I–IV) through phylogenetic analysis. All Hsp70 proteins possessed conserved structural domains, including motif 7, and introns were present in 77.8% of the genes. Chromosomal localization and collinearity analyses of the Hsp70 genes revealed their evolutionary relationships and potential gene duplication events. Examination of the cis-acting elements within the Hsp70 promoter regions revealed that the predominant elements were associated with growth and development, followed by those responsive to hormones, and then elements linked to abiotic stress. Nine genes with high expression were selected for RT-qPCR analysis. Under high-temperature stress, all nine genes were differentially upregulated, and most of these genes belonged to subfamilies II and III, indicating that these two subfamilies have strong potential for heat resistance. In this study, we have elucidated the molecular characteristics and heat response properties of the Hsp70 gene family in P. bournei, revealing the mechanisms behind its heat stress response. Our work provides a reference for stress breeding in P. bournei and a theoretical basis for the exploration of heat tolerance in woody plants.

Adventitious root formation in stem cuttings of Phoebe bournei, an economically and ecologically significant woody species, is a major bottleneck in clonal propagation. To elucidate the impact of spectral quality on early adventitious root development, we characterized the morphological, hormonal, and transcriptomic dynamics of primordium initiation and differentiation under white, red, and blue light. Under red light, cuttings exhibited the earliest and most pronounced formation of white filamentous structures at lenticels, indicative of root primordium initiation, as early as 20 days after cutting, whereas white and blue light treatments showed delayed responses. Paraffin section analysis confirmed the induced origin of root primordia from cortical and vascular cambial tissues, with red light accelerating their differentiation. Hormonal profiling revealed that although red and blue light transiently increased indole-3-acetic acid levels in the basal bark, the persistently elevated abscisic acid in apical buds across all treatments likely suppressed polar auxin transport. Notably, red light downregulated brassinosteroid and gibberellin levels in the base, which could alleviate growth inhibition. Transcriptome analysis of phloem tissues identified significant differential expression of auxin-responsive genes, including members of the ARF (e.g., PbARF6, PbARF13), GH3, and SAUR gene families, which were specifically upregulated under red light. Collectively, our findings suggest that red light accelerates the early induction and differentiation of adventitious root primordia in P. bournei cuttings by modulating hormonal homeostasis and activating key auxin signaling pathways. This work provides a physiological and molecular basis for optimizing light conditions in the vegetative propagation of P. bournei.