Comparative transcriptome profiling of qualitative- and quantitative-specific defense responses underlying the Brassica napus - Leptosphaeria maculans pathosystem
X. ZHANG (1), M. Becker (2), M. Belmonte (2), W. Fernando (1) (1) Department of Plant Science, University of Manitoba, Canada; (2) Department of Biological Sciences, University of Manitoba, Canada; (3) Department of Plant Science, University of Manitoba, Canada

Blackleg caused by the ascomycete fungal pathogen Leptosphaeria maculans is a devastating disease of Brassica napus (rapeseed, canola, oilseed rape). Both major gene (qualitative) resistance and quantitative resistance were identified in B. napus to fight against this pathogen. Our earlier studies uncovered defense mechanisms involved in compatible and incompatible interactions underlying the B. napus-L. maculans pathosystem. However, resistance mechanisms in intermediately resistant cultivars that contributed to quantitative resistance remain unresolved. To elucidate defense mechanisms in intermediate resistance, we performed transcriptional profiling and histological analysis in one B. napus variety, Red River 1861, which demonstrated both qualitative (Rlm2, Rlm3) and quantitative resistance to L. maculans. Seedlings were inoculated with three different L. maculans isolates: AD746 (Av 3-6-(8)-(S)-LepR1), D3 (Av 5-LepR1), and JN3 (Av 1-4-5-6-7-8-(S)) to achieve a complete resistant (incompatible), intermediately resistant, and susceptible (compatible) reactions, respectively. Transcriptome analysis indicated accumulation of a greater number of upregulated genes in quantitative-specific resistance response, whereas less upregulated genes were involved in qualitative-specific response. A set of genes specifically associated with plant defense and phytohormone signaling pathways in quantitative-specific resistance reaction were identified, including genes involved in jasmonic acid signaling pathways, vesicle-mediated transportation, and MAPKKK cascade. Histological analysis of lignin accumulation revealed differences of lignin levels in resistant, intermediately resistant, and susceptible reactions. The results help to unravel key genes and pathways to better understand the defense mechanisms contributing to quantitative resistance.

Abstract Number: P16-483
Session Type: Poster