9.B.197 The Mildew Resistance Locus O (MLO) Family
Mildew resistance Locus O (MLO) proteins are polytopic integral membrane proteins that are plant-specific and primarily concerned with plant-powdery mildew interactions. They have a conserved topology with seven transmembrane domains and an intrinsically unstructured C-terminus. MLO proteins diverged into a family with several clades whose members are associated with different physiological processes. A dataset of MLO amino acyl sequences, comprising nearly all major land plant lineages, has been compiled (Kusch et al. 2016). Seven phylogenetic clades and several MLO peptide motifs that are either conserved in all MLO proteins or confined to one or several clades were identified. Thus, clade-specific diversification of MLO functions is associated with particular sequence motifs. In baker's yeast, some of these motifs are functionally linked to transmembrane transport of organic molecules and ions. MLO-like proteins with highly diverse membrane topologies are present in green and red algae (Rhodophyta), Amoebozoa and Chromalveolata, as well as plants. Putative fusion events between MLO proteins and different kinds of proteins suggest specific MLO functions (Kusch et al. 2016).