Endophytic fungi enhance drought tolerance in Fagopyrum tataricum: Insights into flavonoid biosynthesis and photosynthetic pathways

Fagopyrum tataricum, a nutritionally valuable buckwheat species, is increasingly recognized for its rich flavonoid content. However, its cultivation faces mounting challenges due to drought stress, a problem exacerbated by global climate change. While endophytic fungi have demonstrated potential in enhancing plant drought resistance, their application in F. tataricum and the underlying mechanisms remain underexplored. In this study, two endophytic fungal strains, Botryosphaeria dothidea J46 and Irpex lacteus J79, were isolated and screened for their drought-resistance-promoting effects in F. tataricum. Pot experiments demonstrated successful root colonization of F. tataricum by inoculating these strains under drought conditions. Both Botryosphaeria dothidea J46 and Irpex lacteus J79 promoted root growth, increasing the fresh weight of F. tataricum roots by 49.94 % and 48.80 %, respectively. The content of flavonoids, an important bioactive compound in F. tataricum, was also enhanced. J46 and J79 increased flavonoid content in the leaves of F. tataricum by 28.39 % and 19.54 %, respectively, and in the seeds by 17.79 % and 14.06 %, respectively. Metabolite analysis revealed elevated levels of osmotic regulatory substances and antioxidants, while photosynthetic inhibition caused by drought stress was effectively alleviated upon fungal inoculation. Integrated metabolomic and transcriptomic analyses revealed distinct mechanisms of action for the two strains: B. dothidea J46 upregulated key genes in the flavonoid biosynthesis pathway, including Cinnamate-4-hydroxylase (C4H), Chalcone synthase (CHS), and Chalcone isomerase (CHI), whereas I. lacteus J79 enhanced the expression of genes associated with photosynthesis. Specifically, B. dothidea J46 promotes the plant’s drought resistance by enhancing the expression of genes in the flavonoid biosynthesis pathway, while I. lacteus J79 improves the plant’s photosynthetic efficiency under drought conditions by increasing the activity of genes associated with photosynthesis. Future research will focus on exploring the combined effects of multiple fungal strains, conducting field trials to assess practical applicability, and further elucidating the metabolic pathways involved. This study provides critical insights into the metabolic and molecular mechanisms underlying endophyte-mediated drought resistance, offering a foundation for the development of microbial agents to support the sustainable cultivation of F. tataricum under water-limited conditions.