Transcriptomics reveals the mechanism of branching production in response to GR24 in A. gallica 541

Rhizomorphs are specialized structures formed by the intertwining of mycelia in Armillaria and certain other basidiomycete fungi. The growth and branching of rhizomorphs are essential for nutrient acquisition, host colonization, and environmental adaptation in fungi. Strigolactones (SLs), a class of plant-derived signaling molecules, are well known for their role in promoting hyphal germination and branching in arbuscular mycorrhizal (AM) fungi. Studies suggest that GR24, an SL analogue, may also influence the behavior of other fungi, including Armillaria , promoting the formation of highly specialized rhizomorphs for nutrient acquisition and host colonization. However, the underlying mechanism remains unclear. In this study, we found that rhizomorph branching in GR24-treated A. gallica 541 was significantly greater than in the blank control group (CK). To investigate the response mechanism, we conducted RNA sequencing to examine transcriptomic changes in A. gallica 541 following exogenous GR24 treatment. Differentially expressed gene (DEG) analysis comparing the treated and CK groups revealed 983 differentially expressed genes, including 670 upregulated and 313 downregulated genes. These DEGs were associated with cytochrome P450-related processes, GA synthesis, diterpenoid biosynthesis, NAD(P)-binding proteins, and pentose and glucuronate interconversions. The findings suggest that increased rhizomorph branching is linked to the upregulation of growth-related genes and enhanced carbon metabolism. This study offers new insights into the molecular basis of rhizomorph branching in response to GR24 in A. gallica 541 and highlights the potential role of GR24 in fungal development.