HIGS: Host-Induced Gene Silencing in the Obligate Biotrophic Fungal Pathogen Blumeria graminis    

Abstract

Powdery mildew fungi are obligate biotrophic pathogens that only grow on living hosts and cause damage in thousands of plant species. Despite their agronomical importance, little direct functional evidence for genes of pathogenicity and virulence is currently available because mutagenesis and transformation protocols are lacking. Here, we show that the accumulation in barley (Hordeum vulgare) and wheat (Triticum aestivum) of double-stranded or antisense RNA targeting fungal transcripts affects the development of the powdery mildew fungus Blumeria graminis. Proof of concept for hostinduced gene silencing was obtained by silencing the effector gene Avra10, which resulted in reduced fungal development in the absence, but not in the presence, of the matching resistance gene Mla10. The fungus could be rescued from the silencing of Avra10 by the transient expression of a synthetic gene that was resistant to RNA interference (RNAi) due to silent point mutations. The results suggest traffic of RNA molecules from host plants into B. graminis and may lead to an RNAi-based crop protection strategy against fungal pathogens.

Genome-wide profiling of sRNAs in the Verticillium dahliae-infected Arabidopsis roots

“…The host-induced gene silencing (HIGS) has emerged in application to control plant pathogens, including fungi and oomycetes (Nowara et al 2010; Tinoco et al 2010; Jahan et al 2015; Zhang et al 2016a). Recently, we generated transgenic cotton plants expressing an RNAi construct targeting V. dahliae hydrophobin gene (designed as VdH1i ), and demonstrated the efficiency and effectiveness of producing VdH1i -derived siRNAs in transgenic cotton plants to confer resistance against V. dahliae infection (Zhang et al 2016a).…”

Host-Induced Gene Silencing in Barley Powdery Mildew Reveals a Class of Ribonuclease-Like Effectors

“…This difficulty has been alleviated by the development of host-induced gene silencing (HIGS) (Nowara et al 2010). In barley, this is achieved by particle bombardment of epidermal cells to introduce and transiently express constructs encoding hairpin RNAs corresponding to targeted B. graminis transcripts; the epidermis is then inoculated, and the effect on pathogen development is observed by measuring the haustorial index (HI), i.e., the frequency of full haustorial development relative to empty-vector controls.…”

Genetics and molecular mechanisms of resistance to powdery mildews in tomato (Solanum lycopersicum) and its wild relatives

“…HIGS phenomenon was first observed in barley-Bgh interaction (Nowara et al 2010) and now the idea has provided a method to investigate the role of pathogen genes (Pliego et al 2013). It also suggests a potential approach to engineering plants for resistance to PMs (Nowara et al 2010). …”

“…Whether this host-induced gene silencing (HIGS) degrades fungal transcripts inside the pathogen or inside the plant cells is not certain yet, but the fact that some of the silenced genes function inside the pathogen and also there is no evidence for secretion of Avra10 and AvraK1 transcripts inside epidermal cells, favours the scenario that silencing occurs inside the pathogen (Nowara et al 2010). This phenomenon may suggest the involvement of RNA silencing in plant response to PMs.…”

“…It has been shown that expression of RNAi constructs for Blumeria effectors (Avra10 and AvraK1) and Glucanosyltransferase genes in barley results in a reduction in fungal development (Nowara et al 2010). Whether this host-induced gene silencing (HIGS) degrades fungal transcripts inside the pathogen or inside the plant cells is not certain yet, but the fact that some of the silenced genes function inside the pathogen and also there is no evidence for secretion of Avra10 and AvraK1 transcripts inside epidermal cells, favours the scenario that silencing occurs inside the pathogen (Nowara et al 2010).…”