Characteristics and Diversity of Endophytic Bacteria in Panax Notoginseng Under High Temperature Analysed Using Full-length 16S RRNA Sequencing

Panax notoginseng is a traditional Chinese medicinal herb with diverse properties that is cultivated in a narrow ecological range because of its sensitivity to high temperatures. Endophytic bacteria play a prominent role in plant response to climate warming. However, the endophytic bacterial structures in P. notoginseng at high temperatures are yet unclear. In the present study, the diversity and composition of the endophytic bacterial community, and their relationships with two P. notoginseng plants with different heat tolerance capacities were compared using the full-length 16S rRNA PacBio sequencing system. The results revealed that the diversity and richness of endophytic bacteria were negatively associated with the heat tolerance of P. notoginseng. Beneficial Cyanobacteria, Rhodanobacter and Sphingomonas may be recruited positively by heat-tolerant plants, while higher amounts of adverse Proteobacteria such as Cellvibrio fibrivorans derived from soil destructed the cellular protective barriers of heat-sensitive plants and caused influx of pathogenic bacteria Stenotrophomonas maltophilia. Harmonious and conflicting bacterial community was observed in heat-tolerant and heat-sensitive P. notoginseng, respectively, based on the co-occurrence network. Using functional gene prediction of metabolism, endophytic bacteria have been proposed to be symbiotic with host plants; the bacteria improved primary metabolic pathways and secondary metabolite production of plants, incorporated beneficial endophytes, and combated adverse endophytes to prompt the adaptation of P. notoginseng to a warming environment. These findings provided a new perspective on the function of endophytes in P. notoginseng adaptation to high temperatures, and could pave the way for expanding the cultivable range of P. notoginseng.