Epsilon Open Archive

Abstract

The molecular interaction between two fungal pathogens and their hosts barley (Hordeum vulgare) and Arabidopsis thaliana, are investigated in this thesis. Bipolaris sorokiniana causes spot blotch and common root rot in several cereals including barley. In order to study important defence mechanisms, a set of mutants were generated and studied. The barley lesion mimic mutant Bipolaris sorokiniana tolerant 1 (bst1) has an enhanced tolerance against spot blotch but not root rot. The role of H2O2 was found to be of importance and the gene expression of pathogenesis related (PR) genes were highly up regulated in bst1 after inoculation compared to wild-type. After a new round of mutagenesis and screening, additional germplasm for both root rot and spot blotch caused by B. sorokiniana were identified in bst1 background. Leptosphaeria maculans is the causal agent of blackleg in oilseed crops. In order to study the interaction between L. maculans and a plant host it is more convenient to work with Arabidopsis thaliana. To further investigate the effects of the resistance in Arabidopsis, detailed analyses of mutants in the two TIR-NB-LRR genes in the RLM1 locus and other R gene signalling mutants were made. A quantitative detection system of L. maculans on a genomic level with real time PCR was developed. The analyses showed that RLM1 function is gene dose-dependent under environmental conditions. Analyses on mutants defective in hormone signaling in an rlm1Lerpad3 background revealed significant influence of JA and ET on symptom development as well as pathogen colonization. An important resistance gene, RLM3 was identified from a cross between the highly susceptible accession An-1 and the resistant Col-0 with the use of a microarray analysis. RLM3Col encodes for a TIR and NB protein and has been shown to be of importance for defence to three other necrotrophic fungi (Botryis cinerea, Alternaria brassicicola and A. brassicae). Taken together, this work contributes to enhanced knowledge of interactions between hemibiotrophic fungi and their hosts with a focus on cell death and defence gene responses.