Abstract
The powdery mildew fungus Podosphaera xanthii is one of the most important limiting factors for cucurbit production worldwide. Despite the significant efforts made by breeding and chemical companies, effective control of this pathogen remains elusive to growers. In this work, we examined the suitability of RNAi technology called spray-induced gene silencing (SIGS) for controlling cucurbit powdery mildew. Using leaf disc and cotyledon infiltration assays, we tested the efficacy of dsRNA applications to induce gene silencing in P. xanthii. Furthermore, to identify new target candidate genes, we analyzed sixty conserved and non-annotated proteins (CNAPs) deduced from the P. xanthii transcriptome in silico. Six proteins presumably involved in essential functions, specifically respiration (CNAP8878, CNAP9066, CNAP10905 and CNAP30520), glycosylation (CNAP1048) and efflux transport (CNAP948), were identified. Functional analysis of these CNAP coding genes by dsRNA-induced gene silencing resulted in strong silencing phenotypes with large reductions in fungal growth and disease symptoms. Due to their important contributions to fungal development, the CNAP1048, CNAP10905 and CNAP30520 genes were selected as targets to conduct SIGS assays under plant growth chamber conditions. The spray application of these dsRNAs induced high levels of disease control, supporting that SIGS could be a sustainable approach to combat powdery mildew diseases.
Highlights
Powdery mildew diseases are undoubtedly some of the most important plant diseases worldwide [1]
These discoveries encouraged the development of a novel crop protection strategy designated spray-induced gene silencing (SIGS) that involves the exogenous application of double-stranded RNA (dsRNA) onto plants to silence essential pathogen genes [16,17]
Our results showed that these genes are essential for P. xanthii development and potential targets for RNAi-based approaches and that SIGS could be a promising tool for controlling powdery mildews
Summary
Powdery mildew diseases are undoubtedly some of the most important plant diseases worldwide [1]. Recent works have found that fungal pathogens such as Botrytis cinerea, Fusarium graminearum and Sclerotinia sclerotium can efficiently catch environmental dsRNAs, which are modified into siRNAs and lead the silencing of pathogen genes with complementary sequences [13,14,15] These discoveries encouraged the development of a novel crop protection strategy designated spray-induced gene silencing (SIGS) that involves the exogenous application of dsRNAs onto plants to silence essential pathogen genes [16,17]. The aims of this work were (i) to explore the potential of RNAi technology for cucurbit powdery mildew management by SIGS and (ii) to identify new target candidate genes for this technology For these purposes, we first developed a new and simple gene silencing method for P. xanthii based on the application of dsRNAs to the plant surface. Our results showed that these genes are essential for P. xanthii development and potential targets for RNAi-based approaches and that SIGS could be a promising tool for controlling powdery mildews
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