Can effectoromics and loss-of-susceptibility be exploited for improving Fusarium head blight resistance in wheat?

Bread wheat(Triticum aestiuum L.),which provides about 20%of daily calorie intake,is the most widely cultivated crop in the world,in terms of total area devoted to its cultivation.Therefore,even small increases in wheat yield can translate into large gains.Reducing the gap between actual and potential grain yield in wheat is a crucial task to feed the increasing world population.Fusarium head blight(FHB)caused by the pathogenic fungus Fusaium graminearum and related Fusarium species is one of the most devastating wheat diseases throughout the world.This disease reduces not only the yield but also the quality by contaminating the grain with mycotoxins harmful for humans,animals and the environment.In recent years,remarkable achievements attained in omics"technologies have not only provided new insights into understanding of processes involved in pathogenesis but also helped develop effective new tools for practical plant breeding.Sequencing of the genomes of various wheat patho gens,including F.graminearum,as well as those of bread and durum wheat and their wild relatives,together with advances made in transcriptomics and bioinformatics,has allowed the identification of candidate pathogen effectors and corresponding host resistance(R)and susceptibility(S)genes.However,so far,FHB effectors and wheat susceptibility genes/factors have been poorly studied.In this paper,we first briefly highlighted recent examples of improving resistance against pathogens via new techniques in different host species.We then propose effective strategies towards developing wheat cultivars with improved resistance to FHB.We hope that the article will spur discussions and interest among researchers about novel approaches with great potential for improving wheat against FHB.

RNA silencing in fungi

RNA silencing is an evolutionarily conserved mechanism in eukaryotic organisms induced by double-stranded RNA(dsRNA)and plays an essential role in regulating gene expression and maintaining genome stability.RNA silencing occurs at both posttranscriptional levels through sequence-specific RNA degradation or translational repression and at transcriptional levels through RNA-directed DNA methylation and/or hetero-chromatin formation.RNA silencing pathways have been relatively well characterized in plants and animals,and are now also being widely investigated in diverse fungi,some of which are important plant pathogens.This review focuses primarily on the current understanding of the dsRNA-mediated posttranscriptional gene silencing pro-cesses in fungi,but also discusses briefly the known gene silencing pathways that appear to be independent of the RNA silencing machineries.We review RNA silencing studies for a variety of fungi and highlight some of the mechanistic differences observed in different fungal organisms.As RNA silencing is being exploited as a technology in gene function studies in fungi as well as in engineering anti-fungal resistance in plants and animals,we also discuss the recent progress towards understanding dsRNA uptake in fungi.