Grapevine MLO candidates required for powdery mildew pathogenicity?

MLOs belong to the largest family of seven-transmembrane (7TM) domain proteins found in plants. The Arabidopsis and rice genomes contain 15 and 12 MLO family members, respectively. Although the biological function of most MLO family members remains elusive, a select group of MLO proteins have been demonstrated to negatively regulate defence responses to the obligate biotrophic pathogen, powdery mildew, thereby acting as "susceptibility" genes. Recently we identified a family of 17 putative VvMLO genes in the genome of the cultivated winegrape species, Vitis vinifera. Expression analysis indicated that the VvMLO family members respond differently to biotic and abiotic stimuli. Infection of V. vinifera by grape powdery mildew (Erysiphe necator) specifically upregulates four VvMLO genes that are orthologous to the Arabidopsis and tomato MLOs previously demonstrated to be required for powdery mildew susceptibility. We postulate that one or more of these E. necator responsive VvMLOs may have a role in the powdery mildew susceptibility of grapevine.