Mechanisms Of Plant Immunity Triggered By Beneficial Pseudomonas Strains

The use of beneficial microorganisms for the prevention and control of plant diseases is one of the main alternatives to chemical agents.Beneficial Pseudomonas is the main biological factor,and its rich taxa leads to a variety of mechanisms of action.In this study,we screened and identified fluorescent Pseudomonas strains isolated in the early stage of the laboratory,and obtained four beneficial fluorescent Pseudomonas strains that can stimulate plant immunity.The mechanisms of action of strain 2270 was discussed.The main results are as follows:(1)Immune screening,disease prevention and growth-promoting function tests were carried out on 27 fluorescent Pseudomonas strains selected in the laboratory.Four strains of FP1742,FP1935,2270,and FP2293 with good characteristics were obtained,which could stimulate plant immunity,inhibit the growth of plant pathogens and promote the growth of plants.(2)Complete genomes of four strains were sequenced using the Illumina platform of next-generation sequencing technology,physiological and biochemical identification,genetic evolution analysis,average nucleotide identity(ANI)analysis and DNA-DNA hybridization(DDH)analysis,the results showed that FP2293 is Pseudomonas tolaasii and strains of FP1742,FP1935,2270 may represent new species.(3)Analyze whole genome sequence,which was found that the strains of FP1742,FP1935 and FP2293 have Type III secretion system(T3SS),while strain 2270 does not have T3 SS.The hrcC gene mutation of strains FP1742,FP1935,and FP2293 did not cause plant hypersensitivity,which proved that plant hypersensitive response is related to T3 SS.The spectrum of secondary metabolites of strain 2270 is predicted by anti SMASH,and the results show that it can produce lipopeptides.Two of the gene clusters have high homology with the reported metabolite corpeptin synthesis gene of P.fluorescens In5,It is speculated that it is related to stimulating plant hypersensitive response.(4)Through single-gene and multi-gene knockout of corpeptin homologous genes,the results showed that none of the mutant strains could induce plant hypersensitive response,indicating that this gene cluster played a key role in inducing plant hypersensitive by strain 2270.However,the mutant’s antagonistic ability to pathogenic bacteria did not change.The strain2270 can stimulate the ROS,callose deposition and induce the expression of immune-related genes.The two secondary metabolite gene mutant strains can still triggered the ROS,but lost the ability to induce callosum deposition and expression of immune-related genes NbWRK7,NbWRK8,NbHin-1,and NbHsr203 J.(5)The virus-induced gene silencing(VIGS)system was used to screen the genes involved in the signal transduction pathway of strain 2270 stimulating plant immunity.The result showed that strain 2270 lost the ability to cause hypersensitive response of Nicotiana benthamiana VIGS plants treated with pTRV2-C25 and pTRV2-C28,suggesting that the signal transduction pathway of strain 2270 against diseases is related to C25(Receptor-like protein kinase)and C28(Leucine-rich repeat-containing protein7).In summary,beneficial Pseudomonas can triggered plant immunity through effector proteins secreted by T3 SS and secondary metabolites.The research on the immune mechanism of different strains will help to explore the potential of beneficial Pseudomonas biocontrol,and better develop and apply it to biological control.At the same time,it also laid the foundation for exploring the pathways of beneficial Pseudomonas to participate in plant defense signals.