Abstract
Late blight, caused by the oomycete Phytophthora infestans, is the most important disease of potato (Solanum tuberosum). Understanding the molecular basis of resistance and susceptibility to late blight is therefore highly relevant for developing resistant cultivars, either by marker-assissted selection or by transgenic approaches. Specific P. infestans races having the Avr1 effector gene trigger a hypersensitive resistance response in potato plants carrying the R1 resistance gene (incompatible interaction) and cause disease in plants lacking R1 (compatible interaction). The transcriptomes of the compatible and incompatible interaction were captured by DeepSAGE analysis of 44 biological samples comprising five genotypes, differing only by the presence or absence of the R1 transgene, three infection time points and three biological replicates. 30.859 unique 21 base pair sequence tags were obtained, one third of which did not match any known potato transcript sequence. Two third of the tags were expressed at low frequency (<10 tag counts/million). 20.470 unitags matched to approximately twelve thousand potato transcribed genes. Tag frequencies were compared between compatible and incompatible interactions over the infection time course and between compatible and incompatible genotypes. Transcriptional changes were more numerous in compatible than in incompatible interactions. In contrast to incompatible interactions, transcriptional changes in the compatible interaction were observed predominantly for multigene families encoding defense response genes and genes functional in photosynthesis and CO2 fixation. Numerous transcriptional differences were also observed between near isogenic genotypes prior to infection with P. infestans. Our DeepSAGE transcriptome analysis uncovered novel candidate genes for plant host pathogen interactions, examples of which are discussed with respect to possible function.
Highlights
The oomycete Phytophthora infestans causes late blight disease in Solanaceous plants, in potato (Solanum tuberosum), tomato (Solanum lycopersicum) and their wild relatives
Host resistance to specific races of P. infestans is conferred by single, dominant R genes, which recognize the corresponding avirulence (Avr) gene of P. infestans and trigger a defense response manifesting itself in local cell death, thereby arresting pathogen growth
DeepSAGE libraries We generated fourty four 39 sequence tag libraries from five genotypes, three time points and three biological replicates (one tag library failed (ORF45_3dpi_rep3)) from total RNA extracted from leaf tissue of single plants
Summary
The oomycete Phytophthora infestans causes late blight disease in Solanaceous plants, in potato (Solanum tuberosum), tomato (Solanum lycopersicum) and their wild relatives. Host resistance to specific races of P. infestans is conferred by single, dominant R genes, which recognize the corresponding avirulence (Avr) gene of P. infestans and trigger a defense response manifesting itself in local cell death (hypersensitive resistance, HR), thereby arresting pathogen growth. In this case the host plant and the pathogen are incompatible (incompatible interaction). Depending on the genotype of the host plant, invasion, growth and sporulation of P. infestans progresses with variable efficiency and speed This natural variation of the compatible interaction constitutes another type of resistance, which is controlled by multiple genetic and environmental factors and is called quantitative resistance [14]. Further candidates for quantitative resistance are genes functional in defense signaling [18,19] and defense response genes [20]
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