HYR1-Mediated Detoxification of Reactive Oxygen Species Is Required for Full Virulence in the Rice Blast Fungus

During plant-pathogen interactions, the plant may mount several types of defense responses to either block the pathogen completely or ameliorate the amount of disease. Such responses include release of reactive oxygen species (ROS) to attack the pathogen, as well as formation of cell wall appositions (CWAs) to physically block pathogen penetration. A successful pathogen will likely have its own ROS detoxification mechanisms to cope with this inhospitable environment. Here, we report one such candidate mechanism in the rice blast fungus, Magnaporthe oryzae, governed by a gene we refer to as MoHYR1. This gene (MGG_07460) encodes a glutathione peroxidase (GSHPx) domain, and its homologue in yeast was reported to specifically detoxify phospholipid peroxides. To characterize this gene in M. oryzae, we generated a deletion mutantΔhyr1 which showed growth inhibition with increased amounts of hydrogen peroxide (H2O2). Moreover, we observed that the fungal mutants had a decreased ability to tolerate ROS generated by a susceptible plant, including ROS found associated with CWAs. Ultimately, this resulted in significantly smaller lesion sizes on both barley and rice. In order to determine how this gene interacts with other (ROS) scavenging-related genes in M. oryzae, we compared expression levels of ten genes in mutant versus wild type with and without H2O2. Our results indicated that the HYR1 gene was important for allowing the fungus to tolerate H2O2 in vitro and in planta and that this ability was directly related to fungal virulence

A Bacillus velezensis strain shows antimicrobial activity against soilborne and foliar fungi and oomycetes

Biological control uses naturally occurring antagonists such as bacteria or fungi for environmentally friendly control of plant pathogens. Bacillus spp. have been used for biocontrol of numerous plant and insect pests and are well-known to synthesize a variety of bioactive secondary metabolites. We hypothesized that bacteria isolated from agricultural soil would be effective antagonists of soilborne fungal pathogens. Here, we show that the Delaware soil isolate Bacillus velezensis strain S4 has in vitro activity against soilborne and foliar plant pathogenic fungi, including two with a large host range, and one oomycete. Further, this strain shows putative protease and cellulase activity, consistent with our prior finding that the genome of this organism is highly enriched in antifungal and antimicrobial biosynthetic gene clusters. We demonstrate that this bacterium causes changes to the fungal and oomycete hyphae at the inhibition zone, with some of the hyphae forming bubble-like structures and irregular branching. We tested strain S4 against Magnaporthe oryzae spores, which typically form germ tubes and penetration structures called appressoria, on the surface of the leaf. Our results suggest that after 12 hours of incubation with the bacterium, fungal spores form germ tubes, but instead of producing appressoria, they appear to form rounded, bubble-like structures. Future work will investigate whether a single antifungal molecule induces all these effects, or if they are the result of a combination of bacterially produced antimicrobials

Transcriptome profiling of the rice blast fungus during invasive plant infection and in vitro stresses

<p>Abstract</p> <p>Background</p> <p>Rice blast is the most threatening disease to cultivated rice. <it>Magnaporthe oryzae</it>, its causal agent, is likely to encounter environmental challenges during invasive growth in its host plants that require shifts in gene expression to establish a compatible interaction. Here, we tested the hypothesis that gene expression patterns during <it>in planta </it>invasive growth are similar to <it>in vitro </it>stress conditions, such as nutrient limitation, temperature up shift and oxidative stress, and determined which condition most closely mimicked that of <it>in planta </it>invasive growth. Gene expression data were collected from these <it>in vitro </it>experiments and compared to fungal gene expression during the invasive growth phase at 72 hours post-inoculation in compatible interactions on two grass hosts, rice and barley.</p> <p>Results</p> <p>We identified 4,973 genes that were differentially expressed in at least one of the <it>in planta </it>and <it>in vitro </it>stress conditions when compared to fungal mycelia grown in complete medium, which was used as reference. From those genes, 1,909 showed similar expression patterns between at least one of the <it>in vitro </it>stresses and rice and/or barley. Hierarchical clustering of these 1,909 genes showed three major clusters in which <it>in planta </it>conditions closely grouped with the nutrient starvation conditions. Out of these 1,909 genes, 55 genes and 129 genes were induced and repressed in all treatments, respectively. Functional categorization of the 55 induced genes revealed that most were either related to carbon metabolism, membrane proteins, or were involved in oxidoreduction reactions. The 129 repressed genes showed putative roles in vesicle trafficking, signal transduction, nitrogen metabolism, or molecular transport.</p> <p>Conclusions</p> <p>These findings suggest that <it>M. oryzae </it>is likely primarily coping with nutrient-limited environments at the invasive growth stage 72 hours post-inoculation, and not with oxidative or temperature stresses.</p

Nutritional factors modulating plant and fruit susceptibility to pathogens: BARD workshop, Haifa, Israel, February 25–26, 2018

32 p.-3 fig.The molecular dialog between fungal pathogens and their plant hosts is governed by signals from the plant, secreted pathogen effectors and enzymes, and the plant immune system. There is an increasing awareness that nutritional factors are also central to fungal-plant interactions. Nutritional factors include carbon and nitrogen metabolism, local pH and redox state, and manipulation of host metabolism by secreted pathogen effectors. A diverse combination of approaches from genetics, biochemistry and fungal and plant cell biology addresses these questions, and a workshop whose abstracts accompany this note was held in 2018 to bring these together. Questions were asked about how the lifestyles and nutritional strategies of eukaryotic filamentous phytopathogens are related to the metabolic architectures and pathogenic processes affecting both plant hosts and their pathogens. The aim for future work will be to provide metabolism-based strategies for pathogen control.We thank the US-Israel Binational Agricultural Research and Development Fund (BARD) for funding the workshop (number W-104-17).Peer reviewe

Image_3_A Bacillus velezensis strain shows antimicrobial activity against soilborne and foliar fungi and oomycetes.tif

Biological control uses naturally occurring antagonists such as bacteria or fungi for environmentally friendly control of plant pathogens. Bacillus spp. have been used for biocontrol of numerous plant and insect pests and are well-known to synthesize a variety of bioactive secondary metabolites. We hypothesized that bacteria isolated from agricultural soil would be effective antagonists of soilborne fungal pathogens. Here, we show that the Delaware soil isolate Bacillus velezensis strain S4 has in vitro activity against soilborne and foliar plant pathogenic fungi, including two with a large host range, and one oomycete. Further, this strain shows putative protease and cellulase activity, consistent with our prior finding that the genome of this organism is highly enriched in antifungal and antimicrobial biosynthetic gene clusters. We demonstrate that this bacterium causes changes to the fungal and oomycete hyphae at the inhibition zone, with some of the hyphae forming bubble-like structures and irregular branching. We tested strain S4 against Magnaporthe oryzae spores, which typically form germ tubes and penetration structures called appressoria, on the surface of the leaf. Our results suggest that after 12 hours of incubation with the bacterium, fungal spores form germ tubes, but instead of producing appressoria, they appear to form rounded, bubble-like structures. Future work will investigate whether a single antifungal molecule induces all these effects, or if they are the result of a combination of bacterially produced antimicrobials.</p

Image_1_A Bacillus velezensis strain shows antimicrobial activity against soilborne and foliar fungi and oomycetes.tif

Biological control uses naturally occurring antagonists such as bacteria or fungi for environmentally friendly control of plant pathogens. Bacillus spp. have been used for biocontrol of numerous plant and insect pests and are well-known to synthesize a variety of bioactive secondary metabolites. We hypothesized that bacteria isolated from agricultural soil would be effective antagonists of soilborne fungal pathogens. Here, we show that the Delaware soil isolate Bacillus velezensis strain S4 has in vitro activity against soilborne and foliar plant pathogenic fungi, including two with a large host range, and one oomycete. Further, this strain shows putative protease and cellulase activity, consistent with our prior finding that the genome of this organism is highly enriched in antifungal and antimicrobial biosynthetic gene clusters. We demonstrate that this bacterium causes changes to the fungal and oomycete hyphae at the inhibition zone, with some of the hyphae forming bubble-like structures and irregular branching. We tested strain S4 against Magnaporthe oryzae spores, which typically form germ tubes and penetration structures called appressoria, on the surface of the leaf. Our results suggest that after 12 hours of incubation with the bacterium, fungal spores form germ tubes, but instead of producing appressoria, they appear to form rounded, bubble-like structures. Future work will investigate whether a single antifungal molecule induces all these effects, or if they are the result of a combination of bacterially produced antimicrobials.</p

Image_2_A Bacillus velezensis strain shows antimicrobial activity against soilborne and foliar fungi and oomycetes.tif

Biological control uses naturally occurring antagonists such as bacteria or fungi for environmentally friendly control of plant pathogens. Bacillus spp. have been used for biocontrol of numerous plant and insect pests and are well-known to synthesize a variety of bioactive secondary metabolites. We hypothesized that bacteria isolated from agricultural soil would be effective antagonists of soilborne fungal pathogens. Here, we show that the Delaware soil isolate Bacillus velezensis strain S4 has in vitro activity against soilborne and foliar plant pathogenic fungi, including two with a large host range, and one oomycete. Further, this strain shows putative protease and cellulase activity, consistent with our prior finding that the genome of this organism is highly enriched in antifungal and antimicrobial biosynthetic gene clusters. We demonstrate that this bacterium causes changes to the fungal and oomycete hyphae at the inhibition zone, with some of the hyphae forming bubble-like structures and irregular branching. We tested strain S4 against Magnaporthe oryzae spores, which typically form germ tubes and penetration structures called appressoria, on the surface of the leaf. Our results suggest that after 12 hours of incubation with the bacterium, fungal spores form germ tubes, but instead of producing appressoria, they appear to form rounded, bubble-like structures. Future work will investigate whether a single antifungal molecule induces all these effects, or if they are the result of a combination of bacterially produced antimicrobials.</p