Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

STRUCTURAL AND FUNCTIONAL ANALYSIS OF THE MLO RESISTANCE GENE TO POWDERY MILDEW IN BARLEY

PIFFANELLI P., DEVOTO A., CASAIS C., SCHULZE-LEFERT P.

The Sainsbury Laboratory, Norwich Research Park, Colney, Norwich NR47UH, England, UK

Recessive mlo alleles in barley mediate a broad, non-race-specific resistance reaction to the powdery mildew fungus. Moreover, under pathogen-free conditions, mlo plants exhibit a spontaneous leaf cell death phenotype. Our current working hypothesis is that the wild type Mlo protein has a negative control function in leaf cell death and in pathogen defence. The HvMlo gene was isolated and a large number of Mlo homologues sharing common structural features with the barley gene were identified in other monocots and in Arabidopsis thaliana. The Mlo gene was experimentally shown to encode an integral membrane protein containing 7 transmembrane spanning domains. Biochemical and GFP confocal microscopy studies revealed that Mlo resides in the plasma membrane of barley leaf cells. These features [topology, subcellular localisation and gene family organisation] are structurally reminiscent of G-protein coupled receptors, the largest group of 7 TM proteins in eukaryotes. Genome-wide analysis has unveiled that Mlo-like sequences represent the only family of 7 TM proteins in plants, suggesting that Mlo is the founder of a novel plant-specific family of receptors in higher eukaryotes.

Molecular and biochemical analysis of a number of mlo alleles revealed defects in biogenesis, stability and/or signal transduction of the Mlo protein. These results underline the complexity of events leading to correct folding and efficient signalling mediated by the Mlo protein in barley leaf cells.

A single-cell transient complementation assay was developed to study the relationships between the structure and the resistance function of the Mlo protein. This tool enabled to define that the C-terminal tail represent a critical domain for Mlo function.

This new rapid assay opens the possibility to test if Mlo cereals orthologs are able to functionally complement the mlo barley mutants. These experiments may set the basis to engineering broad-spectrum resistance to powdery mildew in cereals.