Cell Wall Degrading Enzyme Induced Rice Innate Immune Responses Are Suppressed by the Type 3 Secretion System Effectors XopN, XopQ, XopX and XopZ of Xanthomonas oryzae pv. oryzae

Abstract

Innate immune responses are induced in plants and animals through perception of Damage Associated Molecular Patterns. These immune responses are suppressed by pathogens during infection. A number of studies have focussed on identifying functions of plant pathogenic bacteria that are involved in suppression of Pathogen Associated Molecular Pattern induced immune responses. In comparison, there is very little information on functions used by plant pathogens to suppress Damage Associated Molecular Pattern induced immune responses. Xanthomonas oryzae pv. oryzae , a gram negative bacterial pathogen of rice, secretes hydrolytic enzymes such as LipA (Lipase/Esterase) that damage rice cell walls and induce innate immune responses. Here, we show that Agrobacterium mediated transient transfer of the gene for XopN, a X . oryzae pv. oryzae type 3 secretion (T3S) system effector, results in suppression of rice innate immune responses induced by LipA. A xopN - mutant of X . oryzae pv. oryzae retains the ability to suppress these innate immune responses indicating the presence of other functionally redundant proteins. In transient transfer assays, we have assessed the ability of 15 other X . oryzae pv. oryzae T3S secreted effectors to suppress rice innate immune responses. Amongst these proteins, XopQ, XopX and XopZ are suppressors of LipA induced innate immune responses. A mutation in any one of the xopN, xopQ, xopX or xopZ genes causes partial virulence deficiency while a xopN - xopX - double mutant exhibits a greater virulence deficiency. A xopN - xopQ - xopX - xopZ - quadruple mutant of X . oryzae pv. oryzae induces callose deposition, an innate immune response, similar to a X . oryzae pv. oryzae T3S- mutant in rice leaves. Overall, these results indicate that multiple T3S secreted proteins of X . oryzae pv. oryzae can suppress cell wall damage induced rice innate immune responses.

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

“…Thus, it is possible this protein is associated with host cell membranes following secretion. Our observations for XopK are contrasted with the roles of AvrBs2 and XopX, which exhibit reduced virulence phenotypes, consistent with previous studies (Kearney and Staskawicz, 1990;Metz et al, 2005;Zhao et al, 2011;Sinha et al, 2013;Li et al, 2015b;Stork et al, 2015). Our results further illustrate that T3E mutants may impact certain aspects of host-pathogen interactions more than others.…”

“…AvrBs2 contains a glycerol phosphodiesterase domain that is required for its virulence functions in other Xanthomonas pathovars (Kearney and Staskawicz, 1990;Tai et al, 1999;Zhao et al, 2011;Li et al, 2015b). XopX is involved in suppressing pathogen-triggered immunity (Metz et al, 2005;Sinha et al, 2013;Stork et al, 2015). XopK was first identified in the rice pathogen Xanthomonas oryzae pv.…”

Using Ecology, Physiology, and Genomics to Understand Host Specificity inXanthomonas

“…Recent studies highlighted that some T3Es may play a role in suppressing both PTI and ETI. For example, in Xe, XopQ suppresses cell death controlled by the ETI-associated MAP (mitogen-activated protein) kinase MAPKKKa in tomato and pepper (130), whereas in Xoo, XopQ was described to suppress DAMP-induced PTI in rice (120). Another example is that of XopB, which suppresses flg22-induced PTI as well as ETI induced by XopG, AvrBsT, and XopJ in Nicotiana benthamiana (116).…”

Bacterial effector modulation of host E3 ligase activity suppresses PAMP-triggered immunity in rice

“…XopAA Xoo targets OsBAK1, a coreceptor for many PRRs, and OsBRI1, a brassinosteroid receptor, as supported by the observation that transgenic plants expressing XopAA Xoo exhibit a brassinosteroid-insensitive phenotype 21 . In addition, XopN, XopR and XopX also have been shown to suppress host immune responses in plants [22][23][24] 29 . Thus, these recent investigations have revealed that the effectors target key components controlling host immune responses in plants.…”