| Wheat scab and rice blast are important cereal diseases, which can cause devastating yield loss. Their causal agents are Fusarium graminearum and Magnaporthe oryzae, respectively. Studies on the pathogenic mechanisms of these two fungal pathogens can provide theoretical bases for controlling wheat scab and rice blast. Brachypodium distachyon is being developed as a new model for studies on host-pathogen interactions. Brachypodium-Fusarium and Brachypodium-Magnaporthe interaction systems have been established, however, few studies are reported to comprehensively charactering the transcriptional dynamic during Brachypodium-pathogen interactions so far. This study used the dual RNA-seq approach to simultaneously assess the transcriptome profiling of B. distachyon and the fungal pathogens F. graminearum and M. oryzae during their interactions including biotrophic and necrotrophic phases, which can lay foundations for further studies on the molecular mechanisms of the interactions between B. distachyon and these two fungal pathogens. After infection with F. graminearum or M. oryzae, a plenty of defense-related pathways and genes in the diseased tissues were induced and showed distinct temporal dynamics of expression across the infection time course, including genes function in oxidation-reduction process, MAPK cascade, and hormone mediated signaling pathways. For example, besides genes involved in jasmonic acid and ethylene metabolic pathways were up-regulated in infected Brachypodium with both fungi, cytokinin metabolic pathway was induced in Magnaporthe-infected Brachypodium. Reversely, brassinosteroid and gibberelin metabolic pathways were repressed in Fusarium-infected Brachypodium. Each time course-specific processes were signaled. Remarkably, although conserved defense systems were obvious, lots of pathways showed distinct responses during challenge of M. oryzae and F. graminearum, including WRKY transcripton factors and DUF26 RLKs involved in responses to stresses, and ubiquitin-proteasome system involved in protein degradation. We also characterized the pathogen’s transcriptomes. Membrane transporters located in mitochondria were significantly induced during early infection stage. A variety of genes encoding plant cell wall degrading enzymes and secreted proteins were showed to be expressed in specific phase. We identified putative virulence effectors based on their expression dynamic.In addition, a chitin synthase(CHS) gene of M. oryzae was up-regulated during Brachypodium-Magnaporthe interaction. Previous studies showed that fungal CHSs are involved in various cellular progresses including host infection. To unravel the evolutionary relationships of fungal CHS genes and the distribution of CHS genes in different fungal lineages, which can also provide valuable insights for further functional studies on fungal CHS genes, this study systematically identified and compared CHS genes of 109 representative fungi from 18 divergent fungal lineages. The results showed that the fungal CHS gene family is comprised of at least 10 ancestral orthologous clades, which have undergone multiple independent duplications and losses in different fungal lineages during evolution. Notably, one of these CHS clades(class III) was expanded in plant or animal pathogenic fungi belonging to different fungal lineages. Two clades(classes VIb and VIc) identified for the first time in this study occurred mainly in plant pathogenic fungi from Sordariomycetes and Dothideomycetes. Moreover, members of classes III and VIb were specifically up-regulated during plant infection, suggesting important roles in pathogenesis. Furthermore, we identified specificity-determining sites, many of which are located at or adjacent to important structural and functional sites that are potentially responsible for functional divergence of different CHS classes. These sites may be valuable targets for further structural and experimental studies. |
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