Mildew Locus O facilitates colonization by arbuscular mycorrhizal fungi in angiosperms (New Phytol.)

In plants, disease resistance genes typically act in a dominant way – the presence of a resistance allele, even a single copy, is enough to confer resistance. The barley gene Mildew Resistance Locus O (MLO1) is different, as it acts in a recessive way; loss-of-function mlo1 plants are resistant to the pathogenic powdery mildew fungus. Therefore, the presence of MLO1 confers disease susceptibility. Jacott et al. set out to ask why plant genomes carry a gene that makes them more susceptible to disease. Interestingly, they found that mlo1 mutants are also less able to form associations with mycorrhizal fungi, demonstrating a positive benefit for the MLO1 gene, which the authors suggest has been exploited by the pathogen. (Summary by Mary Williams) New Phytol. 10.1111/nph.16465