Folate production by Fusarium sp R2 alleviates water deficit stress in Fagopyrum cymosum

Endophytic fungi can promote host plant growth and enhance resistance during the interaction with the host. The diversity of endophytic fungi inhabiting F. cymosum (a long-used medicinal plant) is unclear, and may alleviate challenges of extreme heat and drought that further its endangered status. This study employed high-throughput sequencing technology to analyze the diversity of endophytic fungi in F. cymosum across different habitats and tissue types. Through correlation analysis and in vitro assays for drought tolerance and growth promotion, three fungal strains with strong drought-resistant and growth-promoting capabilities were identified: Fusarium sp. R2, Ceratobasidium sp. R14, and Colletotrichum sp. L5. The drought tolerance and growth-promoting effects of these strains were further validated by assessing the phenotypic traits and physiological indices of F. cymosum under both soil and hydroponic cultivation conditions. Additionally, non-targeted metabolomic analysis and exogenous folic acid application experiments confirmed that folate is a key metabolite through which Fusarium sp. R2 enhances the drought tolerance of F. cymosum. In conclusion, our study demonstrates that F. cymosum from arid regions harbors a richer diversity of drought-resistant endophytic fungi, and that the Fusarium sp. R2 strain enhances drought resistance by promoting folate metabolism. This discovery reveals part of the underlying mechanisms of drought-resistant fungal strains and holds significant implications for future research on endophytic fungi to addressing agricultural drought issues.