Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2000
Publication Date: N/A
Citation: Interpretive Summary: Fungal diseases cause widespread damage to crop plants. The most efficient way to control these diseases is by the incorporation of genetic resistance to these diseases. We are interested in understanding how an active defense response is triggered so that we can use this information to combat fungal diseases in crops. Resistance to the powdery mildew fungus in barley is conferred by a cluster of genes designated Mla. In this report, we describe the identification of one of these variants, designated Mla1. A novel expression assay was employed to demonstrate the function of this gene. DNA sequence comparison of the Mla1 and Mla6 variants has revealed that the two predicted proteins are highly similar, despite their differences in downstream signaling requirements. Hence, this intriguing interaction between host and pathogen is providing a unique platform from which to explore the subtle features of recognition and signaling specificity. Together with the companion paper describing the Mla6 powder mildew resistance gene (submitted to The Plant Journal), this is the first description of the molecular isolation of a gene that confers resistance to an obligate fungal pathogen in barley. The results described in this manuscript will facilitate research of others that work in the area of resistance gene signaling and molecular pathology as well as the field of plant pathology and molecular breeding.
Technical Abstract: The barley Mla locus encodes 28 characterized resistance specificities to the biotrophic fungal pathogen, Blumeria graminis f sp hordei. We describe a single-cell transient expression assay using entire cosmid DNAs to pinpoint Mla1 within the complex 240 kb Mla locus. The Mla1 cDNA encodes a 108 kDa protein containing a N-terminal coiled-coil structure, a central nucleotide binding domain, and a C-terminal Leucine-rich-repeat region and contains a second short open reading frame at the 5' end which has a possible regulatory function. Although most Mla encoded resistance specificities require Rar1 for their function, we utilize the single-cell expression system to demonstrate that Mla1 triggers full resistance in the presence of the severely defective rar1-2 mutant allele. Wheat contains an orthologue of barley Mla, designated TaMla, which is tightly linked to (0.7 cM) but distinct from the Pm3 locus that encodes many resistance specificities to wheat powdery mildew.