Endophytic bacterial diversity of Vicatia thibetica collected from Xizang and the association with flavonoid accumulation

Vicatia thibetica de Boiss is a unique medicinal and edible plant endemic to Xizang, China. It is one of the five primary root medicines in Tibetan medicine due to its high content of flavonoids. However, the community composition of endophytic bacteria in its various tissues and their potential role in flavonoid accumulation remain unclear. We employed high-throughput sequencing to compare the diversity of endophytic bacteria in the rhizosphere soil and various tissues of V. thibetica collected from three sampling sites in Nyingchi, Xizang. Concurrently, we assessed the types and concentrations of flavonoids present in the roots. Finally, we investigated the relationship between root endophytic bacteria and flavonoid accumulation through correlation analysis. The results indicated that the diversity and abundance of bacterial communities in the rhizosphere soil exceeded those of the endophytic bacterial communities of V. thibetica. Proteobacteria is the dominant phylum, and Sphingomonas is the dominant genus. Each tissue of a plant exhibits its dominant genus. PICRUSt predictive analysis revealed that RNA processing and modification were the predominant functions among related species. Targeted metabolomics analysis has revealed that the roots of the plants contain 14 flavonoid compounds. Correlation analysis revealed that the concentrations of flavonoids in the roots, including apigenin, rutin, astragalin, quercetin 3-glucoside, L-epicatechin, kaempferol, and luteolin, are associated with the distribution and abundance of specific bacterial genera, such as Lactobacillus, Kurthia, Bradyrhizobium, Phenylobacterium, Novosphingobium, and Mycobacterium, among others. This finding suggests that these bacterial genera may directly influence the production and accumulation of flavonoids in the plant. Our findings will enhance the understanding of plant-microbe interactions and provide crucial insights into the role of endophytes in the production of V. thibetica and its significant secondary metabolites.