Endophytic bacteria diversity in different tissues of Polygala sibirica Linnaeus and Polygala crotalarioides Buchanan-Hamilton ex Candolle

Abstract Polygala, a well-known traditional Chinese medicine, has been exploited in large quantities, so it is necessary to take measures to protect, especially P. crotalarioides Buchanan-Hamilton ex Candolle. Endophytic bacteria have significant beneficial effects on plants in promotion of plant growth and biological control, thus high-throughtput sequencing method was used to understand the distribution of endophytic bacteria of Polygala. Results showed that the relative abundance of endophytic bacteria, in descending order, were root, stem and leaf in the two medicinal plants, and that diversity orders were stem, root, leaf in P. sibirica Linnaeus, and leaf, stem, root in P. crotalarioides Buchanan-Hamilton ex Candoll. OTUs were assigned into 23 phyla, of which the predominant phylum was Gammaproteobacteria. Burkholderia-Caballeronia-Paraburkholderia, Acinetobacter, Candidatus_Portiera were predominant in roots, stems and leaves of P. sibirica Linnaeus respectively, while Amycolatopsis in roots and Methylobacterium in stems and leaves were dominant in P. crotalarioides Buchanan-Hamilton ex Candolle. Species correlation analysis showed that phylum Proteobacteria were negatively related to other phyla in the two medicinal plants. Metabolism was the most abundance function, carbohydrate metabolism, amino acid metabolism, metabolism of cofactors and vitamins were the three most abundant metabolic pathways of endophytic bacteria of the two medicinal plants. This was the first report of endophytic bacteria associated to the two medicinal plants, it would offer pivotal information to help explain the reasons of the quality difference of different Polygala species from a new perspective, provide scientific data for the study of the mechanism of plant-microbe interactions and so on.