Study On The Mechanism Of Paenibacillus Polymyxa SC2 Response To Pepper Root Exudates

Paenibacillus polymyxa SC2 isolated from the rhizosphere soil of pepper plant in Guizhou,China showed good antagonistic performance and good ability to promote dissolving phosphorus and dissolving potassium,which has been widely used in pepper,garlic,strawberry,apple and other crops rhizosphere,and play a better role in disease-resistant and relieve continuous cropping obstacles.However,the mechanism of the interaction between SC2 and plants is not clear.We collected the root exudates of pepper and analyzed the effects of root exudates on the growth and chemotaxis of SC2 in the rhizosphere of pepper.Combined with the transcriptome analysis of the interaction between SC2 and pepper root exudates,explored the interactions between pepper root exudates and SC2.In order to study the effect of root exudates on SC2,the root exudates of pepper cultivated in two cases were collected and their components were determined.The results showed that different growth environments had a great influence on the constitute of root exudates,78 and 71 species were detected,respectively,but the two root exudates shared only11 species.The composition of root exudates was very complex,including acids,amino acids,sugars,alcohols,phenols,amines,salts,benzene,ketones,hydrocarbons and esters.Four substances accounting for the highest proportion are acids,amino acids,alcohols and sugars.In this study,we tested the chemotaxis and utilization as nutrition to root exudates and single components of pepper,and found that the root exudates of pepper could not only induce the chemotaxis of SC2 and also serve as the only source of nutrition for SC2 growth and reproduction,which provides strong evidence that root exudates affect bacterial colonization.SC2 exhibits a chemotactic response to most organic acids,amino acids and carbohydrates.Most of the sugar,some organic acids and amino acids can serve as the only nutrient for SC2 to provide energy.However,whether SC2 exhibits a chemotactic response to root exudates and whether root exudates can be used as the only nutrient for the growth and reproduction of the bacteria is not necessarily linked.This experiment proved that the root exudates of peppercould promote the growth and reproduction of SC2,which was beneficial to its colonization in the rhizosphere of pepper.In order to study how PGPR respond to root exudates induce to chemotaxis and colonization in plant rhizosphere and thus play their role in promoting growth and biological control,this study has been carried out a transcriptome sequencing analysis of P.polymyxa SC2 response to pepper root exudates.In this paper,15 min was selected for SC2 interaction with root exudates,which was convenient for observing the early response of bacteria to root exudates.The results showed that a total of 47 genes(0.82%)in SC2 bacterial cells were significantly expression differently in response to the pepper root exudates,among them,37 genes were up-regulated,mainly related to carbohydrate metabolism,transport,quorum sensing and sporulation-related.This result reveals that the P.polymyxa SC2 mainly using nutrients for growth and reproduction at the early stage of contacting with the root exudates of pepper,and the root exudates have a signal and attracting effect on bacteria.Meanwhile,up-regulated of the genes associated with bacterial stress resistance,biofilm and spore formation caused by the root exudates are conducive to the survival and colonization of bacteria.In this paper,the impact of pepper root exudates on the Paenibacillus polymyxa SC2 were studied,the results of the study helped us understand the way bacteria and plants interact in natural conditions,which laid the foundation for the further exploration of the mechanism of bacteria colonization in the rhizosphere of plants.