1.1.25
IDENTIFICATION OF ARABIDOPSIS THALIANA GENES INVOLVED IN RESPONSES TO PHOMA LINGAM

E MÄNTYLÄ, S BOHMAN and C DIXELIUS

Department of Plant Biology, Swedish University of Agricultural Sciences, Box 7080, S-750 07 Uppsala, Sweden

Background and objectives
The fungal disease blackleg, caused by Phoma lingam (sexual stage Leptosphaeria maculans), severely affects canola crops around the world [1]. Very little is known about the mechanisms that make plants resistant to P. lingam. Due to the amenability of Arabidopsis thaliana to dissect such interactions, this plant-pathogen system was developed with the goal of cloning genes of importance for resistance and signal transduction pathways.

Materials and methods
Different approaches have been taken to identify Arabidopsis individuals enabling identification of genes involved in the resistance response. Twenty three ecotypes were screened with four fungal isolates possessing different virulences to Brassica napus. Furthermore, a population of about 12,000 M2 individuals from EMS-treated Ler seeds was screened to find susceptible plants. Another approach that has been taken is the use of insertional mutagenesis by T-DNA to disrupt the resistance gene(s).

Results and conclusions
It was initially found when screening Arabidopsis ecotypes that most were resistant to P. lingam. However, one ecotype was found to be susceptible to isolate PHW 1245. Twelve EMS mutants were also found showing a susceptible phenotype. These plants are being characterized and crossed to ecotype Columbia for detailed mapping and gene cloning. By segregation analysis of an F2 generation it was found that resistance to P. lingam in the A. thaliana rosette leaves is conferred by a single dominant allele. In addition, six T-DNA tagged mutants susceptible to P. lingam have been found. These candidates are now being characterized. Promising mutants will be used in inverted PCR analysis to pick up flanking plant DNA which subsequently can be used as probes in library screenings to identify the genes of interest. Finally, since somatic hybrids between B. napus and A. thaliana were produced [2], offspring from these were thoroughly screened for resistance and examined by use of A. thaliana RFLP markers. From this investigation it can be concluded that the adult leaf resistance gene(s) is/are located on chromosome 3, and the cotyledon resistance is most probably present on chromosome 1 of Arabidopsis.

References
1. Salisbury PA, Ballinger DJ, Wratten N et al., 1995. Australian Journal of Experimental Agriculture 35, 665-672.
2.Forsberg J, Landgren M, Glimelius K, 1994. Plant Science 95, 213-22.