Terpenoids are associated with cytokinin and auxin signaling during mycorrhiza formation in the Suillus bovinus–Pinus yunnanensis symbiosis

Suillus bovinus is an ecologically significant wild ectomycorrhizal fungus that forms symbiotic associations with pine trees. Terpenoids are known to play a key role in interactions between fungi and plants. However, the molecular mechanisms underlying the effects of terpenoids on the formation of symbiotic associations with S. bovinus remain poorly understood. Here, we investigated the effect of S. bovinus terpenoids on root development and mycorrhizal formation in Pinus yunnanensis using physiological, transcriptomic, and phytohormone assays. Our findings revealed that terpenoids from S. bovinus were associated with alterations in the synthesis and signaling of cytokinin in P. yunnanensis, evidenced by changes in the expression of specific genes in the mevalonate synthesis pathway and signaling transduction, such as CKXs, AHP, and A-ARRs. Similarly, these terpenoids correlated with changes in auxin synthesis and signaling, indicated by modulated tryptophan levels and the expression of specific enzyme genes, such as GH3, AUX1, AUX/IAA, and SAUR. This suggests that terpenoids from S. bovinus may contribute to lateral root development and mycorrhizal formation in P. yunnanensis, potentially by influencing the relative levels of cytokinin and auxin. These results shed light on the potential involvement of terpenoids produced by S. bovinus in establishing symbiotic interactions between ectomycorrhizal fungi and their host plants, warranting further direct functional validation.