Abstract
Rhizoctonia solani is an important root infecting pathogen of a range of food staples worldwide including wheat, rice, maize, soybean, potato and others. Conventional resistance breeding strategies are hindered by the absence of tractable genetic resistance in any crop host. Understanding the biology and pathogenicity mechanisms of this fungus is important for addressing these disease issues, however, little is known about how R. solani causes disease. This study capitalizes on recent genomic studies by applying mass spectrometry based proteomics to identify soluble, membrane-bound and culture filtrate proteins produced under wheat infection and vegetative growth conditions. Many of the proteins found in the culture filtrate had predicted functions relating to modification of the plant cell wall, a major activity required for pathogenesis on the plant host, including a number found only under infection conditions. Other infection related proteins included a high proportion of proteins with redox associated functions and many novel proteins without functional classification. The majority of infection only proteins tested were confirmed to show transcript up-regulation during infection including a thaumatin which increased susceptibility to R. solani when expressed in Nicotiana benthamiana. In addition, analysis of expression during infection of different plant hosts highlighted how the infection strategy of this broad host range pathogen can be adapted to the particular host being encountered. Data are available via ProteomeXchange with identifier PXD002806.
Highlights
IntroductionThe specific down-regulation of defense genes in tobacco was observed following R. solani challenge and this could be circumvented by co-inoculation with the biocontrol fungus Trichoderma harzianum which provided enhanced resistance to R. solani [4]
From the ‡CSIRO Agriculture, Floreat, Western Australia; §The University of Western Australia Institute of Agriculture, Crawley, Western Australia; ¶QIMR Berghofer Medical Research Institute, Herston, QLD, Australia
Proteomics analysis of R. solani AG8 under vegetative and infection conditions has been a productive approach to identifying a substantial number of proteins in support of previous gene models, and potential new proteins from six frame translation of the genome
Summary
The specific down-regulation of defense genes in tobacco was observed following R. solani challenge and this could be circumvented by co-inoculation with the biocontrol fungus Trichoderma harzianum which provided enhanced resistance to R. solani [4] These findings suggest R. solani employs an active mechanism to suppress defenses and manipulate the host into susceptibility. Activation of the R proteins induces the plants defenses against biotrophs, including cell death, but in the case of necrotrophs this appears counterproductive and in turn enhances susceptibility to the pathogen. One example of this is the wheat tan spot fungus, Parastagonospora nodorum, which produces a variety of proteinacious host specific toxins including ToxA [11]. A similar situation occurs in Arabidopsis where it is hypothesized that victorin mimics a biotroph effector in order to be recognized by a NBS-LRR R protein, which induces the host cell death defense response and subsequently susceptibility to the pathogen [14]
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