Construction Of Drought-tolerant Microbial Community Of Populus Trichocarpa And Preliminary Study On Its Physiological Mechanism Of Drought-tolerance And Growth Promotion

During the whole life of plants,they are often subjected to many abiotic stresses,of which drought stress is one of the important factors that limit the growth of trees.The growth cycle of trees is long and the trees is difficult to cultivate.In view of its important role in windbreak and sand fixation,protection and greening environment,it is necessary to take a variety of measures to enhance the ability of trees to resist drought stress.The method of using plant growth promoting bacteria to assist plants in drought resistance is gradually accepted by people.Overexpression of the gene Ptr NAC could reduce the pore size of the inner lumen of the xylem vessels in the qualitative part of Populus trichocarpa,increase the number of xylem vessels,and enhance the drought resistance of the plants.Moreover,compared with wild-type Populus trichocarpa(WT),overexpression of OE-Ptr NAC006 showed significantly drought resistance.Studies have reported that different plant genotypes,will recruit different microbial communities.In this study,wild-type Populus trichocarpa(WT)and Ptr NAC gene overexpressed Populus trichocarpa(OE-Ptr NAC006)plants were taken as the research object.The composition and structure of bacterial communities in the root system,rhizosphere soil and peripheral soil of Populus trichocarpa were determined by amplicon sequencing technology.The beneficial strains can promote the growth of Populus trichocarpa under drought stress were analyzed and selected.The drought-tolerant microbial community of Populus trichocarpa sa was constructed and inoculated on wild-type Populus trichocarpa and Arabidopsis thaliana to study the growth-promoting effects of the drought-tolerant microbial community on Populus trichocarpa and Arabidopsis thaliana under drought stress.The main research results are as follows:(1)The amplicon sequencing of microbial communities in root system,rhizosphere soil and peripheral soil of wild-type Populus trichocarpa(WT)and overexpressed Populus trichocarpa(OE-Ptr NAC006)subjected to drought treatment(drought group)and watering treatment(control group)was conducted,and it was found that there were significant differences between α and β diversity analysis of root microbial communities of wild-type Populus trichocarpa(WT)and overexpressed Populus trichocarpa(OE-Ptr NAC006)after drought treatment.The main reason for the drought resistance difference was in the root system of overexpressed Populus trichocarpa(OE-Ptr NAC006)subjected to drought treatment.(2)The relative contents of Pseudomonas,Lactobacillus,and Muribaculaceae in the roots of overexpressed Populus trichocarpa in the control group and the drought group were higher than the relative content of bacteria of the genus in the roots of wild-type Populus trichocarpa.Mean while,the results of LEf Se analysis showed that these bacteria were also the most abundant species in the root system of drought overexpressed Populus trichocarpa(OEPtr NAC006).(3)A resource bank of symbiotic bacteria in the root system and rhizosphere soil of Populus tomentosa was constructed using 10 kinds of culture media,and a total of 1234 bacteria strains were isolated and obtained,among which the dominant bacteria genera were Pseudomonas(21.79%),Bacillus(8.3%)and Arthrobacter(7.54%).Among them,Pseudomonas in the root system and rhizosphere soil of Populus trichocarpa were the dominant strain under water treatment and drought treatment.(4)The enrichment analysis of ASVs at DESeq2 level revealed that the ASVs enriched in the root system of OE-Ptr NAC006 under drought treatment were ASV＿419984,ASV＿222461,ASV＿141107,ASV＿157145,and ASV＿236434,with the classification status of Pseudomonas,Pseudomonas,Lactobacillus,Muribaculaceae,and Pseudomonas.The sequence of each strain in that symbiotic bacteria strain resource bank of the root system and the rhizosphere soil of the Populus trichocarpa was compared with the sequence for enriching ASVs.The results showed that P1(Pseudomonas putida),P2(Pseudomonas koreensis),and P3(Pseudomonas fluorescens)had the highest similarity with ASV＿222461,ASV＿419984,and ASV＿236434.Moreover,these strains were all isolated from the roots of the drought-resistant group.These strains were mixed to construct a drought-tolerant microbial community(namely,microbial community SYN).(5)Under drought stress,Populus trichocarpa and Arabidopsis thaliana inoculated with drought-tolerant microbial community significantly promoted plant growth and significantly increased dry and fresh weight and root length compared with the control group without inoculation.In addition,the plant physiological indicators were also significantly improved,the malondialdehyde(MDA)content was significantly decreased,and the chlorophyll content and antioxidant enzyme(superoxide dismutase(SOD)and peroxidase(POD))activity were significantly increased.In conclusion,in this study,the drought-tolerant microbial community was constructed using DESeq2 enrichment analysis by analyzing the composition and diversity of bacterial microbial communities in the underground part of Populus trichocarpa and constructing the strain database,which provided new ideas for the construction of the microbial community.Under drought stress,inoculating bacterial community into the roots of wild Populus trichocarpa under drought stress can promote the growth of Populus trichocarpa,which is of great significance to improve the growth of trees under drought stress.