Fungal pathogens have evolved antioxidant defense against reactive oxygen species produced as a part of host innate immunity. Recent studies proposed peroxidases as components of antioxidant defense system. However, the role of fungal peroxidases during interaction with host plants has not been explored at the genomic level. Here, we systematically identified peroxidase genes and analyzed their impact on fungal pathogenesis in a model plant pathogenic fungus, Magnaporthe oryzae. Phylogeny reconstruction placed 27 putative peroxidase genes into 15 clades. Expression profiles showed that majority of them are responsive to in planta condition and in vitro H2O2. Our analysis of individual deletion mutants for seven selected genes including MoPRX1 revealed that these genes contribute to fungal development and/or pathogenesis. We identified significant and positive correlations among sensitivity to H2O2, peroxidase activity and fungal pathogenicity. In-depth analysis of MoPRX1 demonstrated that it is a functional ortholog of thioredoxin peroxidase in Saccharomyces cerevisiae and is required for detoxification of the oxidative burst within host cells. Transcriptional profiling of other peroxidases in ΔMoprx1 suggested interwoven nature of the peroxidase-mediated antioxidant defense system. The results from this study provide insight into the infection strategy built on evolutionarily conserved peroxidases in the rice blast fungus.

World wheat production is now under threat due to the wheat blast outbreak in Bangladesh in early March 2016. This is a new disease in this area, indicating the higher possibility of this pathogen spreading throughout the Asia, the world’s largest wheat producing area. Occurrence of this disease caused ~3.5% reduction of the total wheat fields in Bangladesh. Its economic effect on the Bangladesh wheat market was little because wheat contributes to 3% of total cereal consumption, among which ~70% have been imported from other countries. However, as a long-term perspective, much greater losses will occur once this disease spreads to other major wheat producing areas of Bangladesh, India, and Pakistan due to the existing favorable condition for the blast pathogen. The wheat blast pathogen belongs to the Magnaporthe oryzae species complex causing blast disease on multiple hosts in the Poaceae family. Phylogenetic analysis revealed that the Bangladesh outbreak strains and the Brazil outbreak strains were the same phylogenetic lineage, suggesting that they might be migrated from Brazil to Bangladesh during the seed import. To protect wheat production of Bangladesh and its neighbors, several measures including rigorous testing of seed health, use of chemicals, crop rotation, reinforcement of quarantine procedures, and increased field monitoring should be implemented. Development of blast resistant wheat varieties should be a long-term solution and combination of different methods with partial resistant lines may suppress this disease for some time.

Generally, flooding causes waterlogging or submergence stress which is considered as one of the most important abiotic factors that severely hinders plant growth and development. Plants might not complete their life cycle even in short duration of flooding. As biologically intelligent organisms, plants always try to resist or survive under such adverse circumstances by adapting a wide array of mechanisms including hormonal homeostasis. Under this mechanism, plants try to adapt through diverse morphological, physiological and molecular changes, including the closing of stomata, elongating of petioles, hollow stems or internodes, or maintaining minimum physiological activity to store energy to combat post-flooding stress and to continue normal growth and development. Mainly, ethylene, gibberellins (GA) and abscisic acid (ABA) are directly and/or indirectly involved in hormonal homeostasis mechanisms. Responses of specific genes or transcription factors or reactive oxygen species (ROS) maintain the equilibrium between stomatal opening and closing, which is one of the fastest responses in plants when encountering flooding stress conditions. In this review paper, the sequential steps of some of the hormone-dependent survival mechanisms of plants under flooding stress conditions have been critically discussed.

Considering implication of diacylglycerol in both metabolism and signaling pathways, maintaining proper levels of diacylglycerol (DAG) is critical to cellular homeostasis and development. Except the PIP2-PLC mediated pathway, metabolic pathways leading to generation of DAG converge on dephosphorylation of phosphatidic acid catalyzed by lipid phosphate phosphatases. Here we report the role of such enzymes in a model plant pathogenic fungus, Magnaporthe oryzae. We identified five genes encoding putative lipid phosphate phosphatases (MoLPP1 to MoLPP5). Targeted disruption of four genes (except MoLPP4) showed that MoLPP3 and MoLPP5 are required for normal progression of infection-specific development and proliferation within host plants, whereas MoLPP1 and MoLPP2 are indispensable for fungal pathogenicity. Reintroduction of MoLPP3 and MoLPP5 into individual deletion mutants restored all the defects. Furthermore, exogenous addition of saturated DAG not only restored defect in appressorium formation but also complemented reduced virulence in both mutants. Taken together, our data indicate differential roles of lipid phosphate phosphatase genes and requirement of proper regulation of cellular DAGs for fungal development and pathogenesis.