Abstract
Barley mlo mutants are well known for their profound resistance against powdery mildew disease. Recently, mlo mutant plants were generated in hexaploid bread wheat (Triticum aestivum) with the help of transgenic (transcription-activator-like nuclease, TALEN) and non-transgenic (targeted induced local lesions in genomes, TILLING) biotechnological approaches. While full-gene knockouts in the three wheat Mlo (TaMlo) homoeologs, created via TALEN, confer full resistance to the wheat powdery mildew pathogen (Blumeria graminis f.sp. tritici), the currently available TILLING-derived Tamlo missense mutants provide only partial protection against powdery mildew attack. Here, we studied the infection phenotypes of TALEN- and TILLING-derived Tamlo plants to the two hemibiotrophic pathogens Zymoseptoria tritici, causing Septoria leaf blotch in wheat, and Magnaporthe oryzae pv. Triticum (MoT), the causal agent of wheat blast disease. While Tamlo plants showed unaltered outcomes upon challenge with Z. tritici, we found evidence for allele-specific levels of enhanced susceptibility to MoT, with stronger powdery mildew resistance correlated with more invasive growth by the blast pathogen. Surprisingly, unlike barley mlo mutants, young wheat mlo mutant plants do not show undesired pleiotropic phenotypes such as spontaneous callose deposits in leaf mesophyll cells or signs of early leaf senescence. In conclusion, our study provides evidence for allele-specific levels of enhanced susceptibility of Tamlo plants to the hemibiotrophic wheat pathogen MoT.
Highlights
Bread wheat (Triticum aestivum) is one of the worlds most important food crop species [1].Like other cereals, it can suffer from a variety of microbial diseases
We expanded the set of the two triple-mutant lines described before, harboring Tamlo alleles with experimentally determined medium to very strong effects, by selecting independent progenies of respective intermutant crosses [18], resulting in the same allele combinations
We further selected two new triple-mutant lines that are based on Tamlo alleles with experimentally determined weak to strong effects (Figure S1)
Summary
Bread wheat (Triticum aestivum) is one of the worlds most important food crop species [1]. Like other cereals, it can suffer from a variety of microbial diseases. Powdery mildew is a common and widespread disease of angiosperm plants that is caused by ascomycete fungi [3]. These fungi thrive on the basis of an obligate biotrophic lifestyle, i.e., they require living host tissue for growth and reproduction [4]. The causal agent of the disease on these cereals is Blumeria graminis—a species that exists in various highly host-specialized variants (formae speciales; [5]) and has been elected one of the top 10 fungal pathogens in terms of scientific and economic importance [6]
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