Global expression patterns of R-genes in tomato and potato
Janina K. von Dahlen, Kerstin Schulz, Jessica Nicolai, Laura Rose
Abstract
Introduction As key-players of plant immunity, the proteins encoded by resistance genes ( R -genes) recognize pathogens and initiate pathogen-specific defense responses. The expression of some R -genes carry fitness costs and therefore inducible immune responses are likely advantageous. To what degree inducible resistance driven by R -genes is triggered by pathogen infection is currently an open question. Methods In this study we analyzed the expression of 940 R -genes of tomato and potato across 315 transcriptome libraries to investigate how interspecific interactions with microbes influence R -gene expression in plants. Results We found that most R -genes are expressed at a low level. A small subset of R -genes had moderate to high levels of expression and were expressed across many independent libraries, irrespective of infection status. These R -genes include members of the class of genes called NRCs (NLR required for cell death). Approximately 10% of all R -genes were differentially expressed during infection and this included both up- and down-regulation. One factor associated with the large differences in R -gene expression was host tissue, reflecting a considerable degree of tissue-specific transcriptional regulation of this class of genes. Discussion These results call into question the widespread view that R -gene expression is induced upon pathogen attack. Instead, a small core set of R -genes is constitutively expressed, imparting upon the plant a ready-to-detect and defend status.