Science . . . A panoramic view of plant immune response triggered by effect factors.

In the field of plant immunology, PTI (PAMP triggered immunity) and ETI (effector triggered immunity) are very important issues.PRRS located on the surface of cell membrane can recognize PAMPs from pathogens, and then induce further infection of host plant innate immunosuppressive bacteria [1, 2】 Pathogens can bypass or inhibit plant PTI response by secreting protein factors; accordingly, plants have evolved immune factors that specifically recognize effector proteins, such as NLR receptor proteins, which directly or indirectly interact with effector proteins to induce ETI immunity. This process is usually accompanied by severe physiological changes, such as allergic reactions （HR）【3,4】。the immunity mediated by ETI is usually directed against specific pathogens or even specific effectors, while PTI generally shows a broad-spectrum mild resistance mechanism.however, the genotype specificity of ETI reaction and the immune spectrum of different pathogens are not systematically studied.recently, Darrell desveaux and David S. Guttman from the Department of cell and system biology, University of Toronto, Canada, published a research paper entitled the pan genome effector triggered immune landscape of a host pathway interaction in science.in this study, three types of effector mediated ETI phenomenon in the interaction between Pseudomonas syringae and Arabidopsis thaliana were systematically studied by using pan genomics, and a new understanding of the important role of ETI reaction in species specificity of effector recognition was found.in this study, the genomic sequences of 494 Pseudomonas syringae strains from 100 host plants in 28 countries were compared and analyzed by using blastp, and the distribution of three types of effector factors of Pseudomonas syringae was analyzed and summarized. All the effective factor sequences were classified and classified into 70 protein families after a series of sequence alignment optimization There were 622 multi frequency sequence genes.Based on three principles: 1. The upstream 10kbp of the starting codon of the effector contains a conserved HRP box promoter sequence; 2. The sequence of the effector and the upstream region of the HRP box do not contain degenerate bases; 3. The HRP box and its upstream 25bp range of the effector do not contain degenerate bases, and are not at the end of the repeat sequence The gene was synthesized and expressed in the recipient strain for further study of ETI phenotype.to further evaluate the database psytec (Pseudomonas syringae type III effector compendium), the researchers believe that the analysis method in this study can effectively reflect the wide distribution diversity of clove Pseudomonas effect factor family.the second objective of this study was to identify all the effectors in Pseudomonas syringae that could cause ETI response in Arabidopsis thaliana Col-0.529 psytec effectors were expressed in DC3000, and some genes were not normally expressed. Then, Col-0 was screened for infection, and 59 effectors that could induce ETI were identified from 19 protein families. At the same time, similar expression of different effectors reflected the conservation of pathogenic phenotype of immune elicitors in different Heritage background.one representative of 19 protein families was selected to detect the pathogen growth on plants. It was found that the pathogen growth rate with ETI elicitor decreased significantly, which was consistent with the result of ETI reaction.at the same time, the key nucleotides of ETI elicitors were identified, which further confirmed the importance of functional integrity of these proteins in the induction of ETI.HR is a typical phenotype of ETI reaction, but this study found that some obscure HR can still be used as the phenotype of ETI reaction, and there is a strong positive correlation between the intensity of HR and the decline of bacterial growth rate.the researchers evaluated the ETI responses caused by 494 species of Pseudomonas syringae that are theoretically widespread in the world. The main factors affecting the evaluation results are: 1. The expression of different effectors in different strains will affect the ETI response; 2. The effectors expressed on plasmids and chromosomes may have different functions in inducing ETI; 3. The effectors of each psytec branch There is still about 5% amino acid sequence difference, which may lead to the change of ETI effect.the researchers further screened NLRs related to 19 ETI elicitor families in Arabidopsis thaliana, expressed each ETI elicitor in DC3000, then infected different NLR mutant plants, confirmed the corresponding relationship in ETI response through phenotypic experiment, and finally identified the NLR protein that can be induced by all ETI elicitors.screening results confirmed all reported NLR effector combinations, and identified two new NLR genes: at5g18360 (Toll / interleukin-1 receptor can recognize hopB) named bar1 (hopB activated resistance 1) and at1g50180 (rolled coil NLR class can recognize avre and hopaa1) and Car1 (CEL activated resistance) 1) Furthermore, the function of recognizing avre and hopaa1 was further verified by gene editing Car1. the authors believe that NLR gene can be predicted and mapped according to the corresponding relationship between NLRs and ETI elicitors. This study also found that Arabidopsis thaliana is almost immune to Pseudomonas syringae, and only a few resistant NLRs proteins mediate. Eight NLRs resistant proteins may recognize 96.6% of Pseudomonas syringae, At the same time, 68% of the strains could be recognized by multiple NLRs resistant proteins. finally, the researchers studied whether a single NLR protein mediated ETI reaction could determine the specificity of the pathogen in host recognition. compared with the virulent strains pmaes4326 and pmaym7930, it was found that the difference of ETI elicitors between the two strains was mainly due to the presence of hopar1. In the infection experiment, pmaym7930 with hopar1 showed only negligible disease on Col-0, and there were two orders of magnitude differences between pmaes4326 and pmaes4326 in the growth of pathogens on plant leaves, while the growth level of the two pathogens on RPS5 mutant was a few However, the association between pmaicmp2744 and pcbicmp2821 was weak. it is suggested that a single NLR effector interaction combination may determine the specific host immune response to some extent, but not completely. to sum up, this study, through the construction of psytec database, revealed that the highly specific and important ETI reaction in plant immunity was only mediated by a few NLRs in the broad-spectrum host range, and found new potential host pathogen interaction genetic basis, which provided a large number of new targets for broad-spectrum disease resistance breeding. finally, the authors speculate that avoiding ETI reaction may be the key strategy for the pathogen to exert its virulence, and the control of effector dose may also be conducive to the optimization of virulence. references [1] Jones JDG, Dangl JL. 2006. The plant immune system. Nature 444:323 – 29 [2] Zhou JM, Chai J. 2008. Plant pathogenic bacterial type III effectors subdue host responses. Curr. Opin. Microbiol. 11:179–85【3】 Zipfel C. 2009. Early molecular events in PAMP-triggered immunity. Curr. Opin. Plant Biol. 12:414–20【4】Cui, H., Tsuda, K. & Parker, J. E. 2015. Effector-triggered immunity: from pathogen perception to robust Defense. Annu. Rev. Plant Biol. 66, 487 – 511