The diversity of endophytic fungi in Fagopyrum cymosum and the beneficial strain JQ_R2 enhance the host's drought resistance through folate metabolism

Background The emerging field of endophytic fungi studies their capability to enhance host plant growth and resistance through interactions. F. cymosum , a renowned medicinal plant, harbors a diverse yet inadequately understood array of endophytic fungi. Moreover, this plant, already at risk of endangerment, confronts additional threats posed by elevated temperatures and prolonged drought conditions. Hence, we aimed to identify drought-resistant endophytic fungi present in F. cymosum as a potential solution to alleviate this issue. Results The diversity of endophytic fungi across different habitats and tissue sections of F. cymosum was assessed using high-throughput sequencing technology in this investigation. Through correlation analysis, isolation, identification, and in vitro assays, we identified three target strains (JQ_R2, JQ_R14, JQ_L5) demonstrating growth-promotion and drought-resistance activities. These capabilities were subsequently confirmed in soil and hydroponic experiments involving F. cymosum . Transcriptomic and metabolomic analyses indicate that JQ_R2 enhances drought resistance in F. cymosum by boosting basal folate metabolism. Follow-up experiments validated the role of folate in aiding F. cymosum 's drought resistance and demonstrated that the JQ_R2 strain produces folate consistently under both normal and drought conditions. During drought conditions, the dihydrofolate reductase (DHFR) activity of the JQ_R2 strain was substantially increased, suggesting that the JQ_R2 strain enhances drought resistance in F. cymosum , potentially via modulation of the folate metabolism pathway. Conclusions In conclusion, our study illustrates that F. cymosum plants thriving in arid regions host a more diverse array of drought-resistant endophytic fungi, with the JQ_R2 strain augmenting drought resistance in F. cymosum by boosting basal folate metabolism. This finding sheds light on the operational mechanism of drought-resistant fungal strains, bearing considerable importance for forthcoming research on endophytic fungi and mitigating agricultural drought challenges.