Host Delivered RNAi, an efficient approach to increase rice resistance to sheath blight pathogen (Rhizoctonia solani)

Abstract

Rhizoctonia solani, the causal agent of rice sheath blight disease, causes significant losses worldwide as there are no cultivars providing absolute resistance to this fungal pathogen. We have used Host Delivered RNA Interference (HD-RNAi) technology to target two PATHOGENICITY MAP KINASE 1 (PMK1) homologues, RPMK1-1 and RPMK1-2, from R. solani using a hybrid RNAi construct. PMK1 homologues in other fungal pathogens are essential for the formation of appressorium, the fungal infection structures required for penetration of the plant cuticle, as well as invasive growth once inside the plant tissues and overall viability of the pathogen within the plant. Evaluation of transgenic rice lines revealed a significant decrease in fungal infection levels compared to non-transformed controls and the observed delay in disease symptoms was further confirmed through microscopic studies. Relative expression levels of the targeted genes, RPMK1-1 and RPMK1-2, were determined in R. solani infecting either transgenic or control lines with significantly lower levels observed in R. solani infecting transgenic lines carrying the HD-RNAi constructs. This is the first report demonstrating the effectiveness of HD-RNAi against sheath blight and offers new opportunities for durable control of the disease as it does not rely on resistance conferred by major resistance genes.

Pectin induced transcriptome of a Rhizoctonia solani strain causing sheath blight disease in rice reveals insights on key genes and RNAi machinery for development of pathogen derived resistance

“…These genes are an important source of information to further probe the mechanism of RNA silencing pathway in R. solani. The success in the silencing of pathogenicity MAP kinase 1 (PMK1) homologues RPMK1-1 and RPMK1-2 of R. solani through host delivered RNAi could be attributed to the functional RNAi machinery present in R. solani (Tiwari et al 2017).…”

“…The approach of development of cultivars possessing resistance against sheath blight disease has not been very encouraging due to lack of high level of resistance in the available rice germplasm, polygenic nature of the trait of tolerance as well as several unknown complexities associated with resistance phenotype. Though, several researchers have attempted to identify the QTLs (quantitative trait locus) (Channamallikarjuna et al 2010;Silva et al 2012) and few others developed transgenic rice plants by exploiting the genes of host and pathogen to derive the resistance (Datta et al 1999;Sridevi et al 2008;Sripriya et al 2008;Richa et al 2017;Tiwari et al 2017), durable sheath blight resistance is still eluding in rice. Hence, intensive and serious efforts are required to develop effective and durable strategies of resistance against the disease.…”

Understanding sheath blight resistance in rice: the road behind and the road ahead

“…Only recently, two studies showed the successful implication of HIGS in rice– R. solani pathosystem and indicated the presence of the RNA interference system in ShB pathogen (Rao et al , ; Tiwari et al , ). To employ HIGS for controlling ShB, Tiwari et al () targeted pathogenicity map kinase (PMK) genes, while Rao et al () silenced polygalacturonase (PG) gene in R. solani . Interestingly, effective silencing of the pathogen genes has been shown to suppress the ShB disease in the transgenic rice plant carrying the RNAi constructs.…”

“…The success of HIGS largely depends on the existence of a functional RNAi silencing system in the pathogen. Only recently, two studies showed the successful implication of HIGS in rice-R. solani pathosystem and indicated the presence of the RNA interference system in ShB pathogen (Rao et al, 2019;Tiwari et al, 2017).…”

Proteomic and transcriptomic approaches to identify resistance and susceptibility related proteins in contrasting rice genotypes infected with fungal pathogen Rhizoctonia solani

“…Despite extensive efforts, varieties having sufficient level of resistance to ShB could not be developed due to lack of complete resistance in the primary gene pool, and complex and polygenic nature of resistance. Most of the previous efforts have focussed on identification of QTLs (Quantitative Trait Loci) for disease tolerance (Channamallikarjuna et al, 2010;Silva et al, 2012) or developing transgenic rice lines using the host or pathogen genes conferring tolerance (Datta et al, 1999;Richa et al, 2016;Sridevi et al, 2008;Sripriya et al, 2008;Tiwari et al, 2017). However, present state of understanding of the molecular basis of R. solani-rice pathosystem and the major factors (genes/proteins) responsible for establishing the infection by R. solani in rice, are scanty.…”