Magnaporthe oryzae effectors MoHEG13 and MoHEG16 interfere with host infection and MoHEG13 counteracts cell death caused by Magnaporthe-NLPs in tobacco
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Adapted pathogens are able to modulate cell responses of their hosts most likely due to the activity of secreted effector molecules thereby enabling colonisation by ostensible nonhost pathogens.
It is postulated that host and nonhost pathogens of a given plant species differ in their repertoire of secreted effector molecules that are able to suppress plant resistance. We pursued the strategy of identifying novel effectors of Magnaporthe oryzae, the causal agent of blast disease, by comparing the infection process of closely related host vs. nonhost Magnaporthe species on barley (Hordeum vulgare L.). When both types of pathogen simultaneously attacked the same cell, the nonhost isolate became a successful pathogen possibly due to potent effectors secreted by the host isolate. Microarray studies led to a set of M. oryzae Hypothetical Effector Genes (MoHEGs) which were classified as Early- and LateMoHEGs according to the maximal transcript abundance during colonization of barley. Interestingly, orthologs of these MoHEGs from a nonhost pathogen were similarly regulated when investigated in a host situation, suggesting evolutionary conserved functions. Knockout mutants of MoHEG16 from the group of EarlyMoHEGs were less virulent on barley and microscopic studies revealed an attenuated transition from epidermal to mesophyll colonization. MoHEG13, a LateMoHEG, was shown to antagonize cell death induced by M. oryzae Necrosis-and ethylene-inducing-protein-1 (Nep1)-like proteins in Nicotiana benthamiana. MoHEG13 has a virulence function as a knockout mutant showed attenuated disease progression when inoculated on barley.
KeywordsMagnaporthe oryzae Barley Effector proteins Necrosis
The authors are grateful to Nick Talbot, Lauren Ryder (both University of Exeter, UK) and Holger Deising, Ralf Horbach and Jan-Jorrit Krijger (all Martin-Luther-University Halle-Wittenberg, Germany) for introducing Valerie Mogga into Magnaporthe transformation and for sharing material. Didier Tharreau (CIRAD, Montpellier, France) is kindly acknowledged for providing different Magnaporthe isolates. Jochen Kleemann und Richard O’Connell (both MPIPZ, Cologne, Germany) helped with the N. benthamiana infiltration assay and shared material. We are also grateful to Andrew J. Foster (IBWF, Kaiserslautern, Germany) for providing the pCAMB-HPT vector and to Hiromasa Saitoh (Iwate Biotechnology Research Center, Kitakami, Japan) for sharing Δmoheg13 and wild type isolate INA72. Denise Weidenbach was funded in the framework of the Federal Ministry of Education and Research funding activity ‘Plant Biotechnology for the future, PLANT 2030’ within the project ‘BarleyFortress’.
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Conflict of interest
The authors declare that they have no conflict of interest.
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