Analysis of endophytic bacteria diversity between two species of genus Polygala with similar medicinal value.

Polygala is a well-known traditional Chinese medicine, and research is needed to understand how biological approaches can be used to protect this widely cultivated plant. Here, we used high-throughput sequencing methods to understand the distribution of endophytic bacteria, which promote plant growth and act as a biological control in Polygala. We found that endophytic bacteria were most abundant in roots, followed by stems and then leaves in both medicinal plants. Diversity was highest in stems, followed by roots and then leaves in P. sibirica Linnaeus and in leaves followed by stems and then roots in P. crotalarioides Buchanan-Hamilton ex Candoll. OTUs were assigned to 23 phyla, with the phylum Gammaproteobacteria predominating. The main endophytes in the belowground parts of P. sibirica Linnaeus belonged to the genera Burkholderia-Caballeronia-Paraburkholderia and Dyella, with the most common genus in aboveground parts identified as Candidatus Portiera. In P. crotalarioides Buchanan-Hamilton ex Candolle, the main genera in belowground plant parts included the genera Amycolatopsis, Dyella, Actinophytocola, Cupriavidus, and Mycobacterium, and the genera Methylobacterium, Novosphingobium, Sphingomonas, and Curtobacterium were the main genera in aboveground parts. This work represents the first report of endophytic bacteria associated with the two medicinal plants. It offers a new perspective to understand differences in quality between Polygala species and provides data to support better understanding of the mechanisms underlying plant-microbe interactions.