1.1.14
DOWNY MILDEW OF ARABIDOPSIS THALIANA: ANALYSIS OF RESISTANCE RESPONSES OF THE ECOTYPE WS TO THE WELA ISOLATE OF PERONOSPORA PARASITICA

C KRUSE, HG EIBEN and AJ SLUSARENKO

RWTH Aachen, Institut fuer Biologie III (Pflanzenphysiologie), 52056 Aachen, Germany

Background and objectives
Peronospora parasitica causes downy mildew on Arabidopsis thaliana. The WELA isolate of P. parasitica used in this work is virulent on the Arabidopsis ecotypes La-er and Wei-0, but avirulent on Col-0, RLD and Ws. A population of T-DNA tagged lines of Ws was screened to find mutants to susceptibility. One such mutant, called mutant D, was found which had lost resistance to the WELA isolate of P. parasitica but was still resistant to the NOCO isolate. The right border of the T-DNA with an associated fragment of plant DNA was cloned by plasmid rescue and used to isolate the wild-type locus from an l-DASHTM Ws genomic library. The ca15-kb genomic wild-type locus was transformed into the mutant and into two susceptible ecotypes (La-er and Wei-0). Seed from the primary transformants was sown out and inoculated with WELA, and the segregating T1 plants showed individuals with resistant phenotypes [1]. Resistance phenotypes ranged from a clear HR to arrested pathogen growth at various stages with very little associated necrosis. Sequencing of the ca 3.3-kb locus in which the T-DNA insertion was located revealed that the tagged gene was not a classical RPP locus [1] but that it showed ca 50% identity to an IAA-leucine amidohydrolase gene ILR1 already cloned from Arabidopsis [2]. Plants transformed with a genomic clone containing a truncated version of the wt locus tagged by the T-DNA in mutant D showed no such resistant individuals. Homozygous transformed lines of the complemented mutant and the ecotypes Wei-0 and La-er have been selected and characterized microscopically for their resistance phenotypes to the WELA isolate of P. parasitica.

Results and conclusions
Shorter transformation constructs were prepared from the original 15-kb clone and used to transform Arabidopsis ecotypes and tobacco to see if resistance to downy mildew can be engineered into other crops. We have called the tagged gene GR1. Results of a comparison of the behaviour of mutant D and ilr1 on medium containing different IAA-amino acid conjugates will be presented, along with a comparison of the response of the two mutants to infection with WELA. Data concerning the effects of wounding and jasmonic acid on the expressoin of GR1 will also be presented.

References
1. Rempulska Bujas G, 1996. Dissertation, Universität Zürich.
2. Bartel B, Fink GR, 1995. Science 268, 1745-1748.