3.4.33
TOWARDS THE MOLECULAR ISOLATION OF RARI, A GENE REQUIRED FOR RACE-SPECIFIC RESISTANCE TO POWDERY MILDEW IN BARLEY

TLA HAYE1, K SHIRASU 1 and P SCHULZE-LEFERT1

1The Sainsbury Laboratory, John lnnes Centre, Colney Lane, Norwich NR4 7UH, UK

Background and objectives
The Mla-12 gene in barley confers race-specific resistance to the powdery mildew fungus Erysiphe graminis f.sp. hordei. Two loci required for the function of Mla-12 specified resistance, designated Rar1 and Rar2 (required for Mla-12 specified resistance), have been characterised in our laboratory [1]. Both genes are necessary for triggering a cell death reaction during an early stage of infection and both control the temporal accumulation pattern of defence-related gene transcripts upon pathogen challenge. A map-based cloning approach has been initiated to isolate the Rarl1 locus.

Results and conclusions
DNA markers which are either tightly linked or co-segregate with the target locus have been identified and enabled us to construct a local high resolution genetic map on the basis of more than 8000 meiotic events. Using CAPS markers an interval of 0.7 cM was determined including the target gene and a cosegregating RFLP marker was used to identify four YAC clones containing inserts of 330, 680, 720 and 1100 kb, respectively. Isolation and mapping of YAC ends enabled us to establish a local YAC contig which delimits Rar1 within 330 kb on a single YAC clone. Twelve recombinants were identified in the 330 kb chromosomal interval containing Rar1. These recombinants provide the basis to further narrow down physically the target region. BAC sub-libraries from the YACs have been constructed. BAC clones adjacent to the marker co-segregating with Rar1 have been isolated and a local BAC contig was established. We have initiated DNA sequencing of those clones and the results from this analysis will be presented.

References
1. Freialdenhoven A, Scherag B, Holiricher K et al., 1994. Plant Cell 6, 983-94.