Transcriptional Up-Regulation of GrapevineMLOGenes in Response to Powdery Mildew Infection

Abstract

Mildew resistance locus o (MLO) proteins are plant-specific seven-transmembrane (7TM) proteins that are thought to play a role in vesicle trafficking to the plasma membrane. Certain members of the <i>MLO</i> gene family are required for powdery mildew (PM) fungi (Erysiphales) to establish a pathogenic interaction with their plant hosts. Such <i>MLO</i> genes increase in transcription in response to PM infection, and the loss of their function confers broad-spectrum resistance to PM pathogens in barley, tomato, and <i>Arabidopsis thaliana.</i> In this study, a 17-member <i>MLO</i> gene family has been identified in the genome sequence of <i>Vitis vinifera</i>. Fourteen genes of the <i>VvMLO</i> family have been shown to be transcribed at various levels in shoot tips, flower buds, flowers, and leaves. Two <i>VvMLO</i>s increased in transcription in response to the grapevine-adapted PM fungus <i>Erysiphe necator</i>. The predicted polypeptides encoded by these two PM-responsive <i>VvMLOs</i> clustered in the same phylogenetic clade as AtMLO2, AtMLO6, and AtMLO12, proteins that are required by the PM fungus <i>Golovinomyces orontii</i> for causing disease on <i>A. thaliana.</i> The PM-responsiveness of these grapevine genes and their relatedness to <i>AtMLO</i>s suggest that a grapevine <i>MLO</i> gene (or genes) may also be involved in the pathogenesis of <i>E. necator</i>.