Mildew Locus O facilitates colonization by arbuscular mycorrhiza in angiosperms

O_LILoss of barley Mildew Resistance Locus O (MLO) is known to confer durable and robust resistance to powdery mildew (Blumeria graminis), a biotrophic fungal leaf pathogen. Based on the increased expression of MLO in mycorrhizal roots and its presence in a clade of the MLO family that is specific to mycorrhizal-host species, we investigated the potential role of MLO in arbuscular mycorrhizal interactions. C_LIO_LIUsing mutants from barley, wheat, and Medicago truncatula, we demonstrate a role for MLO in colonization by the arbuscular mycorrhizal fungi Rhizophagus irregularis. C_LIO_LIEarly mycorrhizal colonization was reduced in mlo mutants of barley, wheat and Medicago truncatula, and this was accompanied by a pronounced decrease in the expression of many of the key genes required for intracellular accommodation of arbuscular mycorrhizal fungi. C_LIO_LIThese findings suggest that the primary role of MLO in angiosperms is in the establishment of symbiotic associations with beneficial fungi, which has been appropriated by powdery mildew. C_LI