Tempered mlo broad-spectrum resistance to barley powdery mildew in an Ethiopian landrace

Xintian Ge,Weiwei Deng,Simon R Ellwood,Patrick Schweizer,Zheng Zhou Lee,Francisco J Lopez-Ruiz

doi:10.1038/srep29558

Abstract

Recessive mutations in the Mlo gene confer broad spectrum resistance in barley (Hordeum vulgare) to powdery mildew (Blumeria graminis f. sp. hordei), a widespread and damaging disease. However, all alleles discovered to date also display deleterious pleiotropic effects, including the naturally occurring mlo-11 mutant which is widely deployed in Europe. Recessive resistance was discovered in Eth295, an Ethiopian landrace, which was developmentally controlled and quantitative without spontaneous cell wall appositions or extensive necrosis and loss of photosynthetic tissue. This resistance is determined by two copies of the mlo-11 repeat units, that occur upstream to the wild-type Mlo gene, compared to 11–12 in commonly grown cultivars and was designated mlo-11 (cnv2). mlo-11 repeat unit copy number-dependent DNA methylation corresponded with cytological and macroscopic phenotypic differences between copy number variants. Sequence data indicated mlo-11 (cnv2) formed via recombination between progenitor mlo-11 repeat units and the 3′ end of an adjacent stowaway MITE containing region. mlo-11 (cnv2) is the only example of a moderated mlo variant discovered to date and may have arisen by natural selection against the deleterious effects of the progenitor mlo-11 repeat unit configuration.

Highlights

Recessive mutations in the Mlo gene confer broad spectrum resistance in barley (Hordeum vulgare) to powdery mildew (Blumeria graminis f. sp. hordei), a widespread and damaging disease
Successive rounds of wide scale monocultures leads to isolates harbouring large numbers of virulence genes, with virulence to almost all resistance gene (R-gene) deployed in Europe present in just two isolates[4]
Partial resistance is common in plants but often absent in modern barley cultivars, where genetic bottlenecks and breeding between elite cultivars has led to extinction of diversity in some genomic regions and increased linkage disequilibrium[5,6]

Summary

Introduction

Recessive mutations in the Mlo gene confer broad spectrum resistance in barley (Hordeum vulgare) to powdery mildew (Blumeria graminis f. sp. hordei), a widespread and damaging disease. Recessive resistance was discovered in Eth[295], an Ethiopian landrace, which was developmentally controlled and quantitative without spontaneous cell wall appositions or extensive necrosis and loss of photosynthetic tissue This resistance is determined by two copies of the mlo-11 repeat units, that occur upstream to the wild-type Mlo gene, compared to 11–12 in commonly grown cultivars and was designated mlo-11 (cnv). Powdery mildews are a group of fungal diseases caused by obligate biotrophic species (species that derive nutrients from living tissue) Their distribution is world-wide and they infect most staple crops. The commonest form of resistance in plants to biotrophic fungi follows the race-specific gene-for-gene principle first demonstrated by Flor[2], where recognition is governed by the direct or indirect interaction between the product of a host disease resistance gene (R-gene) and the complementary product of a pathogen avirulence gene[3]. Two are currently known: RPW8, identified in Arabidopsis conferring resistance to diverse www.nature.com/scientificreports/

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