Orchid seeds lack endosperms and depend on mycorrhizal fungi for germination and nutrition acquisition under natural conditions. Piriformospora indica is a mycorrhizal fungus that promotes seed germination and seedling development in epiphytic orchids, such as Dendrobium nobile. To understand the impact of P. indica on D. nobile seed germination, we examined endogenous hormone levels by using liquid chromatography–mass spectrometry. We performed transcriptomic analysis of D. nobile protocorm at two developmental stages under asymbiotic germination (AG) and symbiotic germination (SG) conditions. The result showed that the level of endogenous IAA in the SG protocorm treatments was significantly higher than that in the AG protocorm treatments. Meanwhile, GA₃ was only detected in the SG protocorm stages. IAA and GA synthesis and signaling genes were upregulated in the SG protocorm stages. Exogenous GA₃ application inhibited fungal colonization inside the protocorm, and a GA biosynthesis inhibitor (PAC) promoted fungal colonization. Furthermore, we found that PAC prevented fungal hyphae collapse and degeneration in the protocorm, and differentially expressed genes related to cell wall metabolism were identified between the SG and AG protocorm stages. Exogenous GA₃ upregulated SRC2 and LRX4 expression, leading to decreased fungal colonization. Meanwhile, GA inhibitors upregulated EXP6, EXB16, and EXP10-2 expression, leading to increased fungal colonization. Our findings suggest that GA regulates the expression of cell wall metabolism genes in D. nobile, thereby inhibiting the establishment of mycorrhizal symbiosis.

Euryodendron excelsum H. T. Chang, a monotypic plant endemic to China, exhibits significant variations in adventitious root formation in cuttings across different age groups through unclear molecular mechanisms. In this study, we performed RNA-sequencing (RNA-seq) and data analysis at three stages—initial excision (S0), root primordia (S1), and emergence of adventitious roots (S2)—for lateral buds from transplanted triennial tissue culture seedlings and decennial E. excelsum plants. We identified 13,424 differentially expressed genes (DEGs) between different rooting stages and age groups, including 8216 upregulated and 5208 downregulated genes. A Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis indicated that the S1 and S2 DEGs identified were mainly involved in phenylpropanoid biosynthesis, plant hormone signal transduction, plant–pathogen interactions, biosynthesizing various secondary plant metabolites, and starch and sucrose metabolism. Key auxin-pathway genes were expressed at significantly higher levels in culture seedlings than in adult plants, as were WUSCHEL-related homeobox and LATERAL ORGAN BOUNDARIES DOMAIN genes (related to adventitial root growth and development), which together promote the formation, growth, and development of adventitial root primordia. The dysregulated expression of 15 DEGs identified by RNA-seq were verified via real-time quantitative polymerase chain reaction analysis. This study investigates the morphological processes of adventitious root formation in cuttings of E. excelsum of different ages, and the potential molecular mechanisms involved. Our finding provides a basis for research on cutting propagation, conservation applications, and optimization of tissue culture for E. excelsum, and may help improve the rooting rate of E. excelsum cuttings.