Comparison Of The Growth-promoting Effects And Mechanisms Of Two Plant Endophytic Bacteria

Endophytes can establish harmonious synbiosis with host plants and they become new kind of microbial resources.On the one hand,plants can provide endophytes with stable living space,on the other hand,endophytes can promote plants growth and improve plants resistance to stress.A lot of reports showed that,most endophytes or root microorganism with the abilities of growth promotion and increase of plant resistance have ACC deaminase activity.Whether is the growth promotion mainly related to the ACC deaminase?The effect and its molecular mechanism are not sure.DLJ1(Pseudomonasfluorescens biovar I,from pepper fruit with high ACC deaminase activity)and SZ5(Bacillus cereus,from ripe persimmon,with medium ACC deaminase activity),which were found by our lab,have different activities of ACC deaminase.They can promote the growth of chili plants,improve the resistance of the plants to Moledogyne ingnita.We don't know whether they still have the effect of growth promotion under normal conditions.Whether they can improve the resistance of chili plants to other environmental stress and whether the mechanism of their growth promotion is related to ACC deaminase activity are not unclear.So,effect of two endophytes under normal conditions and their molecular mechanism about growth promotion and increase of resistance to waterlogging will be analysed.in this paper.Results are as follows:1.Conparison of growth,metabolism and yield between pepper plants pretreated with two endophytes.The inoculation treatment during germination could promote plant photosynthetic efficiency,and increase antioxidant enzymes activity,reduce the accumulation of ROS,inprove activities of plant chitinase and lipoxygenase activity,and nhance their fruit yields under natural conditions in the field.Inoculation during germination showed a better effect than inoculation during transplanting.Inoculation several times didn't show better effects.The effects of DUI was better than those of SZ5.Results above showed that both endophytes could promote pepper plants growth and DLJ1 had more significant effects.2.Colrparison of gene expression between pepper plants pretreated with endophytes.Using the transcriptome analysis technology,the difference of gene expression between pepper plants pretreated with two endophytes was analyzed to find the similarities and differences of their mechanisms.GO and KEGG enrichment results showed that both endophytes reduced the expressions of genes related to the ethylene signaling pathway and DLUI showed a higher effect than SZ5 did.DLJ1 treatment also significantly improved expressions of genes related to plant photosynthesis and antioxidant and reduced expression of genes related to the secondary metabolism.SZ5 treatment didn't show evident effect about photosynthesis,antioxidance and secondary substance metabolism Gene expression analysis verified the results from field experim on molecular level It proved that DLJ1 can promote photosynthesis and plant growth through decreasing the ethylene effect and secondary substance metabolism.It suggested that their effects might be small when plants are under the stress which highly related to ethylene.3.The influence of DLJ1 on pepper seedings under waterlogging.Pepper seedings,which were pretreated with DLJ1 during germination,were treated with waterlogging stress and the ethylene receptor inhibitor STS were used to detect whether pretreatment by DLJ1 can reduced plants resistance to ethylene stress and the waterlogging stress.Results showed that DLJ1 pretreatment significantly increased the plants resistance to waterlogging when without treatment of STS.The CK group perished after being sprayed with STS,while the DLJ1 group showed a better performance.Comprehensive physiological results suggested that plant growth and tpllants resistance to stress are closely related to ethylene metabolism.Ethylene lcontent decreased by ACC deaminase,its resistance to waterlogging decreased in DLJ1 group.After treated with STS,the resistance of both groups to watertogging decreased,and both of their ethylene pathways were supressed.But DLJ1 group revealed a relatively high resistance to watertogging which might due to its high photosynthetic and antioxidant ability.These results proved once again that DLJ1 with ACC deaminase activity has the ability to promote plants grow,but the suppression of ethylene pathway may decrease the resistance to some stress.he promotion effects on plant growth and stress resistance of endophytes,which can produce ACC deaminase are closed related to its ACC deaminase activities.