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MoVam7, a conserved SNARE involved in vacuole assembly, is required for growth, endocytosis, ROS accumulation, and pathogenesis of Magnaporthe oryzae.

ABSTRACT: Soluble NSF attachment protein receptor (SNARE) proteins play a central role in membrane fusion and vesicle transport of eukaryotic organisms including fungi. We previously identified MoSce22 as a homolog of Saccharomyces cerevisiae SNARE protein Sec22 to be involved in growth, stress resistance, and pathogenicity of Magnaporthe oryzae. Here, we provide evidences that MoVam7, an ortholog of S. cerevisiae SNARE protein Vam7, exerts conserved functions in vacuolar morphogenesis and functions in pathogenicity of M. oryzae. Staining with neutral red and FM4-64 revealed the presence of abnormal fragmented vacuoles and an absence of the Spitzenkörper body in the ΔMovam7 mutant. The ΔMovam7 mutant also exhibited reduced vegetative growth, poor conidiation, and failure to produce the infection structure appressorium. Additionally, treatments with cell wall perturbing agents indicated weakened cell walls and altered distributions of the cell wall component chitin. Furthermore, the ΔMovam7 mutant showed a reduced accumulation of reactive oxygen species (ROS) in the hyphal apex and failed to cause diseases on the rice plant. In summary, our studies indicate that MoVam7, like MoSec22, is a component of the SNARE complex whose functions in vacuole assembly also underlies the growth, conidiation, appressorium formation, and pathogenicity of M. oryzae. Further studies of MoVam7, MoSec22, and additional members of the SNARE complex are likely to reveal critical mechanisms in vacuole formation and membrane trafficking that is linked to fungal pathogenicity.

SUBMITTER: Dou X

PROVIDER: S-EPMC3025985 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The oxidative degradation of lipids through lipid peroxidation processes results in the generation of free fatty acid radicals. These free radicals including reactive oxygen species (ROS) serve as a substrate for generating reactive aldehydes. The accumulation of free fatty acid radicals, ROS, and reactive aldehydes in cell compartments beyond physiological threshold levels tends to exert a damaging effect on proximal membranes and distal tissues. Living organisms deploy a wide array of efficient enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and aldehyde dehydrogenases (ALDHs) for scavenging reactive molecules and intermediates produced from membrane lipid peroxidation events. Although the contributions of SOD, CAT, and POD to the pathogenesis of microbial plant pathogens are well known, the influence of ALDH genes on the morphological and infectious development of plant pathogenic microbes is not well understood. In this study, we deployed RNA interference (RNAi) techniques and successfully silenced two putative family-four aldehyde dehydrogenase genes potassium-activated aldehyde dehydrogenase (MoKDCDH) and delta-1-pyrrorine-5-carboxylate dehydrogenase (MoP5CDH) in the rice blast pathogen Magnaporthe oryzae. The results obtained from the phenotypic analysis of individual knock-down strains showed that the RNAi-mediated inactivation of MoKDCDH and MoP5CDH triggered a significant reduction in conidiogenesis and vegetative growth of ΔMokdcdh and ΔMop5cdh strains. We further observed that downregulating the expression of MoKDCDH and MoP5CDH severely compromised the pathogenesis of the rice blast fungus. Also, the disruption of MoKDCDH and MoP5CDH M. oryzae undermined membrane integrity and rendered the mutant strains highly sensitive to membrane stress inducing osmolytes. However, the MoKDCDH and MoP5CDH knock-down strains generated in this study displayed unaltered cell wall integrity and thus suggested that family-four ALDHs play a dispensable role in enforcing cell wall-directed stress tolerance in M. oryzae. From these results, we deduced that family-four ALDHs play a conserved role in fostering membrane integrity in M. oryzae possibly by scavenging reactive aldehydes, fatty acid radicals, and other alcohol derivatives. The observation that downregulating the expression activities of MoKDCDH had a lethal effect on potential mutants further emphasized the need for comprehensive and holistic evaluation of the numerous ALDHs amassed by the rice blast fungus for their possible engagement as suitable targets as antiblast agents.

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MoVam7, a conserved SNARE involved in vacuole assembly, is required for growth, endocytosis, ROS accumulation, and pathogenesis of Magnaporthe oryzae.

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