Disease-Specific Gene Expression in Tomato Leaves

Gene transcriptional changes can provide information on the plant response to biotic and abiotic stresses. Measuring gene expression could help making early and invisible stress symptoms detectable. Plants are non-hosts or resistant to most pathogenic organisms. In many cases they react to an incompatible pathogen either with a general or specific reaction leading to resistance. But what happens when a compatible pathogen attacks, leading to disease? Major questions are (1) can the plant recognize and react specifically to each of the pathogens? (2) How are the regulated genes expressed within time and space? Pathogen- and mock-inoculated tomato leaf samples were subjected to Illumina transcriptome sequencing with 3-fold experimental replicates. Whole transcriptomes of the early (24 hours post inoculation) interaction of susceptible tomato (Solanum lycopersicon) leaves with its major pathogens Phytophthora infestans, Oidium neolycopersici and Botrytis cinerea led to the identification of disease-specific gene regulation patterns. Running a standard pairwise differential expression analysis and EBSeq – an empirical Bayes hierarchical model comparing all disease- and mock-inoculated samples – we identified 28 up-regulated and 22 down-regulated genes in tomato leaves inoculated with B. cinerea as well as 18 up-regulated genes in leaves inoculated with P. infestans. Leaves inoculated with O. neolycopersici appeared healthy both in terms of visible symptoms as well as at the gene expression level. The level of differential regulation, their function and putative use for disease detection will be discussed.