Cross-Kingdom RNAi of Pathogen Effectors Leads to Quantitative Adult Plant Resistance in Wheat

Luisa Katharina Schaefer,Thomas Wicker,Gabriele Buchmann,Esther Jung,Jonas Stehlin,Roman Schmid,Marion Claudia Müller,Francis Parlange,Salim Bourras,Beat Keller,Gerhard Herren,Andreas Wehrli

doi:10.3389/fpls.2020.00253

Luisa Katharina Schaefer, Thomas Wicker + Show 10 more

Open Access

https://doi.org/10.3389/fpls.2020.00253

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Abstract

Cross-kingdom RNA interference (RNAi) is a biological process allowing plants to transfer small regulatory RNAs to invading pathogens to trigger the silencing of target virulence genes. Transient assays in cereal powdery mildews suggest that silencing of one or two effectors could lead to near loss of virulence, but evidence from stable RNAi lines is lacking. We established transient host-induced gene silencing (HIGS) in wheat, and demonstrate that targeting an essential housekeeping gene in the wheat powdery mildew pathogen (Blumeria graminis f. sp. tritici) results in significant reduction of virulence at an early stage of infection. We generated stable transgenic RNAi wheat lines encoding a HIGS construct simultaneously silencing three B.g. tritici effectors including SvrPm3a1/f1, a virulence factor involved in the suppression of the Pm3 powdery mildew resistance gene. We show that all targeted effectors are effectively downregulated by HIGS, resulting in reduced fungal virulence on adult wheat plants. Our findings demonstrate that stable HIGS of effector genes can lead to quantitative gain of resistance without major pleiotropic effects in wheat.

Highlights

RNA interference (RNAi) is a biological process in which small non-coding RNAs are employed to selectively downregulate gene expression at the transcriptional or post-transcriptional level
We showed that host-induced gene silencing (HIGS) can be used in stable transgenic wheat plants to effectively target three B.g. tritici effectors
The stable transgenic events generated in this study constitutively express the SvrPm3a1/f 1-RNAi transgene

Summary

Introduction

RNA interference (RNAi) is a biological process in which small non-coding RNAs (sRNAs) are employed to selectively downregulate gene expression at the transcriptional or post-transcriptional level. While miRNAs correspond to 20–22-nt sequences typically derived from imperfect RNA hairpin structures, siRNAs refer to 20–24-nt sequences typically processed from long double-stranded RNA (dsRNA) precursors (Borges and Martienssen, 2015; D’Ario et al, 2017). Both siRNAs and miRNAs are processed from dsRNA precursors by the ribonuclease Dicer, and both can regulate gene expression. RNAi participates in the regulation of diverse biological processes including plant immunity (Brant and Budak, 2018; Deng et al, 2018), and several siRNAs and miRNAs have been described as important players in plant defense against viruses, bacteria, and fungi (Hua et al, 2018; Rosa et al, 2018; Muhammad et al, 2019)

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