A Preliminary Study On The Interaction Mechanism Between Two Plant-growth Promoting Rhizobacteria Strains And Peanut

Peanut is one of the main oil crops in the world,and the planting area of China ranks first in the world.The large application of chemical fertilizer can increase the yield,but it will cause environmental problems.However,drought and salt stress also cause serious damage to peanut,and reduce its yield and quality.Plant growth-promoting Rhizobacteria(PGPR)is an effective means to enhance plant stress resistance and increase yield.Two strains of PGPR,Tsukamurella Tyrosinosolvens P9 and Burkholderia Pyrrocinia P10,were used as research objects in this study.The effects of the two strains on the growth and antioxidant defense system of peanut under normal water condition,drought and salt stress were analyzed by pot experiments.The root exudates of peanut were collected by hydroponics method to study the effects of root exudates on gene expression and metabolic pathway of two strains of PGPR,so as to explore the interaction mechanism between P9,P10 strain and peanut.The results are as follows:Setting P9,P10 and P9+P10 mixed strain inoculation treatments.Under normal water conditions,the three inoculated treatments all increased the root length,plant height and fresh weight of peanuts on different levels,and reduced the proline content of seedlings.Leaf relative water content,malondialdehyde(MDA)content,superoxide dismutase(SOD),peroxidase(POD),and catalase(CAT)have no obvious difference.Drought inhibits the growth of peanut seedlings,reduces the chlorophyll content and the relative leaf water content,but these strain's treatments can increase the chlorophyll content and leaf water content of seedlings,reduce the content of malondialdehyde,so as to enhance the drought resistance and promote the growth of plants.Similarly,salt stress can inhibit the growth of peanuts,resulting in a decrease in chlorophyll content,and an increase in malondialdehyde content,proline content and H₂O₂level.However,after inoculated with PGPR strains,the growth index and chlorophyll content of seedlings were higher than those of non-inoculated plants,and malondialdehyde content and H₂O₂level were lower.These inoculated treatment reduced the reactive oxygen species(ROS)level and H₂O₂content of peanuts under salt stress,and reduced the effect of free radical accumulation on tissue cells and enhance salt resistance of peanuts.When 2%and 1%root exudate of peanuts were added to the culture medium,P9 and P10strains were then inoculated and cultured for 22h and 2h(both in logarithmic growth phase),respectively,the growth of the two PGPR strains could be significantly promoted.Transcriptomics sequencing analyzed the effect of root exudates on the gene expression of the two strains.The results showed that there were 126 differentially expressed genes in P9 strain,of which 81 were up-regulated and 45 were down-regulated genes;the differential genes were mainly enriched in 17significantly different pathways.Except for the down-regulation of arginine biosynthesis,the up-regulated pathways mainly focus on catabolic pathways and biosynthesis.The P10 strain has491 differentially expressed genes,of which 462 are up-regulated and 29 are down-regulated genes;these differential genes are mainly enriched in 8 pathways with significant differences,Five pathways,including ABC transporter,siderophore group non-ribosomal peptides,steroid degradation,quorum sensing,and galactose metabolism,are significantly up-regulated pathways,and the three significantly down-regulated pathways are flagella assembly,fructose and mannose metabolism,alanine,aspartic acid,and glutamate metabolism.12 genes of P9 strain and 12 genes of P10 strains related to the growth and growth-promoting characteristics were selected for Real Time Quantitative PCR(RT-q PCR),and the results showed the same expression trend as the transcriptome analysis.In summary,on the one hand,the two PGPR strains can promote the growth of peanut under normal conditions,drought and salt stress,and improve the stress resistance of peanut seedlings.On the other hand,affected by root exudates,it is speculated that the two strains have different gene expressions in material and energy metabolism,material transport,siderophore synthesis,virulence and quorum sensing,flagella and bacterial motility,etc.,and promote The growth and reproduction of strains and the play of their growth-promoting properties.