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

• Main Authors: Katrin Gruner, Tobias Esser, Johanna Acevedo-Garcia, Matthias Freh, Michael Habig, Roxana Strugala, Eva Stukenbrock, Ulrich Schaffrath, Ralph Panstruga
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: Genes
• Subjects: <i>Blumeria graminis</i>; hexaploid bread wheat; <i>Magnaporthe oryzae</i>; <i>Mlo</i>; plant disease resistance; powdery mildew
• Online Access: https://www.mdpi.com/2073-4425/11/5/517

Barley <i>mlo</i> mutants are well known for their profound resistance against powdery mildew disease. Recently, <i>mlo</i> mutant plants were generated in hexaploid bread wheat (<i>Triticum aestivum</i>) 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 <i>Mlo</i> (<i>TaMlo</i>) homoeologs, created via TALEN, confer full resistance to the wheat powdery mildew pathogen (<i>Blumeria graminis</i> f.sp. <i>tritici</i>), the currently available TILLING-derived <i>Tamlo</i> missense mutants provide only partial protection against powdery mildew attack. Here, we studied the infection phenotypes of TALEN- and TILLING-derived <i>Tamlo</i> plants to the two hemibiotrophic pathogens <i>Zymoseptoria tritici</i>, causing Septoria leaf blotch in wheat, and <i>Magnaporthe oryzae</i> pv. <i>Triticum</i> (<i>MoT</i>), the causal agent of wheat blast disease. While <i>Tamlo</i> plants showed unaltered outcomes upon challenge with <i>Z. tritici</i>, we found evidence for allele-specific levels of enhanced susceptibility to <i>MoT</i>, with stronger powdery mildew resistance correlated with more invasive growth by the blast pathogen. Surprisingly, unlike barley <i>mlo</i> mutants, young wheat <i>mlo</i> 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 <i>Tamlo</i> plants to the hemibiotrophic wheat pathogen <i>MoT</i>.