Analysis of new type III effectors from Xanthomonas uncovers XopB and XopS as suppressors of plant immunity

Abstract

Summary The pathogenicity of the Gram‐negative plant‐pathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) is dependent on type III effectors (T3Es) that are injected into plant cells by a type III secretion system and interfere with cellular processes to the benefit of the pathogen. In this study, we analyzed eight T3Es from Xcv strain 85‐10, six of which were newly identified effectors. Genetic studies and protoplast expression assays revealed that XopB and XopS contribute to disease symptoms and bacterial growth, and suppress pathogen‐associated molecular pattern (PAMP)‐triggered plant defense gene expression. In addition, XopB inhibits cell death reactions induced by different T3Es, thus suppressing defense responses related to both PAMP‐triggered immunity (PTI) and effector‐triggered immunity (ETI). XopB localizes to the Golgi apparatus and cytoplasm of the plant cell and interferes with eukaryotic vesicle trafficking. Interestingly, a XopB point mutant derivative was defective in the suppression of ETI‐related responses, but still interfered with vesicle trafficking and was only slightly affected with regard to the suppression of defense gene induction. This suggests that XopB‐mediated suppression of PTI and ETI is dependent on different mechanisms that can be functionally separated.

Transcriptomic analysis reveals tomato genes whose expression is induced specifically during effector-triggered immunity and identifies the Epk1 protein kinase which is required for the host response to three bacterial effector proteins

“…A number of genes described previously as involved in incompatible plant-pathogen interactions were found to be specifically induced during ETI, supporting the idea that gene expression differences are a useful way to distinguish the two immune responses [9]. Several previous studies have used reporter genes as a readout for activation of PTI and its subsequent suppression by pathogen effectors [44][45][46][47]. Reporter genes for PTI have also been developed for tomato and N. benthamiana [5,48,49].…”

Quantitative, image-based phenotyping methods provide insight into spatial and temporal dimensions of plant disease

“…This phenotype demonstrates the importance of a pathogen's ability to establish infection for overall virulence. While XopK is a predicted T3E effector that carries the hallmarks of a secreted virulence factor (Furutani et al, 2006;Furutani et al, 2009;Schulze et al, 2012), its roles during infection appear to be complex. The XopK protein sequence contains 54% hydrophobic residues and several predicted transmembrane domains.…”

“…Previous data indicated that XopK is secreted through the type III secretion system into host cells (Furutani et al, 2009;Schulze et al, 2012). Although the xopK gene is conserved in many Xanthomonas species, its role in virulence is unknown (Bogdanove et al, 2011;Potnis et al, 2011;Bart et al, 2012;Schulze et al, 2012;Arrieta-Ortiz et al, 2013;Jalan et al, 2013).…”

Xanthomonas campestris pv. vesicatoria Secretes Proteases and Xylanases via the Xps Type II Secretion System and Outer Membrane Vesicles

“…vesicatoria, we performed transcript studies with strains 85-10 and 85-10hrpG* (85*), which contains HrpG*, a constitutively active version of HrpG (49). HrpG is the key regulator of the T3S genes and also activates the expression of T2S genes (8,(50)(51)(52). Yet, the expression of the T2S substrate gene XCV0965 is suppressed by HrpG, as was shown in our previous study (8).…”