mlo‐based powdery mildew resistance in hexaploid bread wheat generated by a non‐transgenic TILLING approach

Abstract

SummaryWheat is one of the most widely grown cereal crops in the world and is an important food grain source for humans. However, wheat yields can be reduced by many abiotic and biotic stress factors, including powdery mildew disease caused by Blumeria graminis f.sp. tritici (Bgt). Generating resistant varieties is thus a major effort in plant breeding. Here, we took advantage of the non‐transgenic Targeting Induced Lesions IN Genomes (TILLING) technology to select partial loss‐of‐function alleles of TaMlo, the orthologue of the barley Mlo (Mildew resistance locus o) gene. Natural and induced loss‐of‐function alleles (mlo) of barley Mlo are known to confer durable broad‐spectrum powdery mildew resistance, typically at the expense of pleiotropic phenotypes such as premature leaf senescence. We identified 16 missense mutations in the three wheat TaMlo homoeologues, TaMlo‐A1, TaMlo‐B1 and TaMlo‐D1 that each lead to single amino acid exchanges. Using transient gene expression assays in barley single cells, we functionally analysed the different missense mutants and identified the most promising candidates affecting powdery mildew susceptibility. By stacking of selected mutant alleles we generated four independent lines with non‐conservative mutations in each of the three TaMlo homoeologues. Homozygous triple mutant lines and surprisingly also some of the homozygous double mutant lines showed enhanced, yet incomplete, Bgt resistance without the occurrence of discernible pleiotropic phenotypes. These lines thus represent an important step towards the production of commercial non‐transgenic, powdery mildew‐resistant bread wheat varieties.

Mechanisms of powdery mildew resistance of wheat – a review of molecular breeding

“…Mild temperatures (10–22 °C) further enhance the infection process (Beest et al , 2008). Upon adhesion of conidia or ascospores to a photosynthetically active wheat leaf surface, a specialized germ tube is produced and elongates to form a thread‐like hypha with appressoria and this process can complete within 2 hr (Acevedo‐Garcia et al , 2017). Shortly afterwards, the digitate hypha gives rise to a penetration peg and ramifies a haustorium to allow the breach of the host epidermal cell, via turgor pressure and dynamic enzymes (Glawe, 2008).…”

Molecular breeding technologies and strategies for rust resistance in wheat (Triticum aestivum) for sustained food security

“…TILLING was also employed to screen a mutant population of the Chinese wheat cultivar Sumai 3 in the map‐based cloning of Fhb1 , which confers head blight disease resistance (Rawat et al ., ). In addition, powdery mildew resistant wheat lines were developed using TILLING technology to select the mlo mutants (Acevedo‐Garcia et al ., ). The homozygous triple and double mutant lines showed enhanced resistance to powdery mildew without pleiotropic effects, suggesting that TILLING could be used to develop commercial wheat varieties.…”

Identification and Expression Analysis of Fragaria Vesca MLO Genes Involved in Interaction with Powdery Mildew (Podosphaera Aphanis)

“…Recently, Acevedo Garcia et al [24] identified simultaneous mutations in the three wheat homologues of TaMlo, TaMlo-A1, TaMlo-B1 and TaMlo-D1 and produced homozygous triple and double mutant lines that showed increased resistance to powdery mildew. In another study, the knock-down of grapevine MLO genes (VvMLO7 in combination with VvMLO6 and VvMLO11) decreased powdery mildew severity up to 77 % [25].…”