Functional Importance Of Aldehyde Dehydrogenase In The Filamentous Ascomycete Magnaporthe Oryzae

Plants are endowed with the capability rapidly synthesize numerous,and diverse groups secondary metabolites,including,hydrogen peroxides,aldehydes and other alcohol derivatives in response to persistent irritations induced by intruding pathogenic microbes.These secondary metabolites represent genetically inducible host resistance parameter and have been largely regarded as one of the most effective and earliest defense mechanism,which is readily activated in host plants in a bid to ward off invading pathogens and hence promoting host immunity.Operationally,this form of resistance which is generally referred to as pathogen-triggered immunity(PTI)involves the rapid generation and accumulation these highly reactive metabolites at the site of infection which in turn functions as direct reactive substrates that are lethal enough to kill pathogens,inhibit growth and development of the pathogen in the host cell.Among these secondary metabolites,aldehydes and its alcohol derivatives constitutes the most abundant chemical arsenal deployed by host plants against parasitic microbes and obviously plant pathogens must adequately overwrite this innate resistance or defense barriers posed by host plants in an attempt to establish compatible interaction necessary for the development of disease in their host plants.To understand how the possible mechanisms engaged by plant pathogenic fungi to nullify this vast array of aldehydes in host cells during the host-pathogen interaction,we subsequently employed bio informatics,functional genomics and proteomic approaches to take inventory,evaluate the pathophysiological functions and identify putative interacting proteins of aldehyde dehydrogenases(ALDHs)Magnaporthe oryzae.Aldehyde dehydrogenases are an evolutionarily conserved group of polymorphic enzyme(isozyme)and belong to a superfamily of NAD(P)(+)-dependent enzymes,which catalyses the irreversible oxidation of endogenous and exogenous aldehydes to their corresponding carboxylic acids and hence fundamentally responsible for the detoxification of inter-and extra-cellular aldehydes.Members of the aldehyde dehydrogenase superfamily are greatly diverse and are localized in different cellular compartments.They also participate in various metabolic and biosynthetic pathways.We strongly believed that this research is relevant and timely,owing to the fact that,since the early 18th century when first incidence rice blast epidemic was recorded in Asia,the rapidly evolving blast pathogen has spread across over 86 rice producing regions globally and yield losses huge enough to feed more than 60 million rice consumers annually vis-a-vis the urgent need to increase the present level of rice production from the current production level of 500 million tons to 700 million ton using limited labour,water and cultivation space,unarguably showed that the rice blast fungus constitutes the greatest threat undermining the realization of household,national and global food security.From our sequence BLAST search,we identified 16 putative aldehyde dehydrogenase genes in the publicly available genome data resource of Magnaporthe oryzae and proceeded to examine the phylogenetic history of the identified aldehyde dehydrogenase genes in the rice blast fungus and their counterpart in other pathogenic and non-pathogenic fungi.A total of 13 genes belonging to the aldehyde dehydrogenase superfamily in the globally destructive rice blast fungus M.oryzae were successfully deleted or silenced using homologous recombination or RNAi respectively.We further subjected the various deletion mutants to series of bioassays to ascertain the contributions of the successfully compromised aldehyde dehydrogenase genes to the physiological and morphological development of the rice blast fungus.Corresponding results obtained from this study showed that vast majority of the aldehyde dehydrogenases identified in.the M.oryzae genome promotes cell proliferation and enhances the development of vegetative growth.Additionally,we observed that all the aldehyde dehydrogenase genes investigated in this research are crucially required for conidiation and hence,defective mutants displayed a significant decline with regards to the quantum of conidia produced.More so,it emerged that all the substrate specific aldehyde dehydrogenase successfully evaluated during this study thus,Methylmalonate-semialdehyde dehydrogenase(MoMET),Fatty aldehyde dehydrogenase(MoFAT)and Salicylaldehyde dehydrogenase(MoSAL)are vital for the pathogenicity of the rice blast fungus and as a result their subsequent deletion rendered the resultant mutants were non-pathogenic on both rice and barley seedlings.Furthermore,we have shown for the first time that,MoMET specifically regulates the development of germ tube and infectious structures by modulating important signalling pathways implicated in the development of appressorium in As a result,?Momet null mutants exhibited sprouting of abnormal germ tubes in a rattoon-like manner.We also showed here that,aldehyde dehydrogenase mutants generated in our study are exclusively sensitive to alcohol but,exhibited moderate to strong resilience against other osmolytes including reactive oxygen species(ROS),sodium dodecyl sulphate(SDS),sodium chloride(NaCl)and dithiothreitol(DTT).Outcomes from this study with regards to broad substrate aldehyde dehydrogenases showed that most of these broad substrate aldehyde dehydrogenases,although contributes to virulence of the blast fungus,they,however,does not disrupt the pathogenicity.Conversely,two of the broad substrate aldehyde dehydrogenases encoded by MGG 00719 and MGG 07890 have been identified in our study as pathogenicity factors,and their deletion mutants were non-pathogenic on both host and non-host plants.Furthermore,we observed that Potassium-activated aldehyde dehydrogenase(MoPot)was required for conidia-morphogenesis in M.oryzae and in evidence AMopot knock-down mutants generated in our study were characterised with the generation of conidia with abnormal morphology and loss of pathogenicity.Finally,we noticed that aldehydes dehydrogenase in M.oryzae functions as osmo-protectant and as a consequence most deletion mutants generated during this study were associated with high incidence of cell burst.Given that,total or partial impairment of the various aldehyde dehydrogenases evaluated over the course of this study remarkably interfered in the physiology,pathogenicity and virulence of the rice blast fungus,provided enough iota to conclude that,the high number of aldehyde dehydrogenases amassed by the rice blast fungus could be effectively explored as targets for developing potent and durable anti-blast agents.