Abstract
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.
Highlights
Aldehydes are intermediates in several fundamental metabolic pathways, including the synthesis of carbohydrates, vitamins, steroids, amino acids, and lipids (Kirch et al, 2004)
We identified a total of 16 Aldehyde dehydrogenases (ALDHs) (MoALDH)-encoding genes in the rice blast fungus genome and further demonstrated that 12 of the 16 ALDHs identified in M. oryzae have multiple copies (Norvienyeku et al, 2017)
Aldehyde dehydrogenases (ALDHs) are an evolutionarily conserved group of NAD/NADP-dependent multigenic enzymes that are involved in the irreversible oxidation of endogenous and exogenous reactive aldehydes to their nontoxic corresponding carboxylic acids (Dong et al, 2017; Li et al, 2017; Norvienyeku et al, 2017)
Summary
Aldehydes are intermediates in several fundamental metabolic pathways, including the synthesis of carbohydrates, vitamins, steroids, amino acids, and lipids (Kirch et al, 2004). ALDHs belong to a superfamily of NADP+-dependent enzymes that are involved in the irreversible oxidation of endogenous and exogenous aldehydes to their corresponding carboxylic acids (Zhang et al, 2012; Luo et al, 2015; Buchman and Hurley, 2017). A total of 19 dehydrogenase-encoding genes have been recorded in the human genome. Insights gained from these previous studies showed that human ALDHs play critical cellular and biological roles including detoxification of aldehydes, cell proliferation, peroxidation of membrane lipid, protection of tissues against hyperosmotic pressure, and inhibition of tumors and cancers (Januchowski et al, 2013; Morgan and Hurley, 2015)
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