Evidence for Allele-Specific Levels of Enhanced Susceptibility of Wheat mlo Mutants to the Hemibiotrophic Fungal Pathogen Magnaporthe oryzae pv. Triticum

Barleymlomutants are well known for their profound resistance against powdery mildew disease. Recently,mlomutant 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 wheatMlo(TaMlo) homoeologs, created via TALEN, confer full resistance to the wheat powdery mildew pathogen (Blumeria graminisf.sp.tritici), the currently available TILLING-derivedTamlomissense mutants provide only partial protection against powdery mildew attack. Here, we studied the infection phenotypes of TALEN- and TILLING-derivedTamloplants to the two hemibiotrophic pathogensZymoseptoria tritici, causing Septoria leaf blotch in wheat, andMagnaporthe oryzaepv.Triticum(MoT), the causal agent of wheat blast disease. WhileTamloplants showed unaltered outcomes upon challenge withZ. tritici, we found evidence for allele-specific levels of enhanced susceptibility toMoT, with stronger powdery mildew resistance correlated with more invasive growth by the blast pathogen. Surprisingly, unlike barleymlomutants, young wheatmlomutant 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 ofTamloplants to the hemibiotrophic wheat pathogenMoT.