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.

Rice blast caused by Magnaporthe oryzae pathotype is the worst disease that leads to serious food insecurity globally. Understanding rice blast disease pathogenesis is therefore essential for the development of a blast disease mitigation strategy. Reverse phosphorylation mediated by phosphatases performs a vital function in the activation of diverse biological mechanisms within eukaryotic. However, little has been reported on the roles of PP2Cs in the virulence of blast fungus. In this current work, we deployed functional genomics and biochemical approaches to characterize type 2C protein phosphatase MoPtc6 in blast fungus. Deletion of MoPTC6 led to a drastic reduction in conidiophore development, conidia production, hyphal growth, and stress tolerance. Western blotting assay demonstrated that the phosphorylation level of MoOsm1 was decreased while MoMps1 was increased in the MoPtc6 deletion mutant, and comparative transcriptome assay revealed a higher number of expressed genes between mutant and wild type. Localization assay confirmed that MoPtc6 is sub-localized in the cytoplasm of mycelia, spores, and in the appressoria of M. oryzae. Furthermore, disruption of MoPTC6 impaired appressoria turgor pressure and glycogen utilization; more findings revealed attenuation of hyphal penetration and virulence upon deletion of MoPTC6. Generally, present findings suggested the role of MoPtc6 in the growth and virulence of M. oryzae.

Protein phosphatases are crucial enzymes that regulate key cellular processes such as the cell cycle, gene transcription, and translation in eukaryotes. Seven PP2C protein phosphatases have been identified in Magnaporthe oryzae. However, their synergistic roles in the pathology and physiology of M. oryzae remain poorly investigated. By qRT-PCR analysis, we found that PTC1 and PTC2 are significantly upregulated in the PTC5 deletion mutant. The double deletion of the MoPTC5/MoPTC1 and MoPTC5/MoPTC2 genes significantly reduced hyphal growth, conidiophore formation, sporulation, and virulence in M. oryzae. In addition, the double-knockout mutants were increasingly sensitive to different osmotic, oxidative, and cell wall stresses. Western blot analysis revealed that MoPtc5 plays a synergistic function with MoPtc1 and MoPtc2 in the regulation of MoMps1 and MoOsm1 phosphorylation levels. Lastly, appressorium formation and turgor generation were remarkably affected in the ΔMoptc5ΔMoptc1 and ΔMoptc5ΔMoptc2 double-deletion mutants. These findings demonstrate the overlapping roles of PP2c protein phosphatase in the fungal development and pathogenesis of M. oryzae.