Global expression patterns of -genes in tomato and potato.

Introduction: As key-players of plant immunity, the proteins encoded by resistance genes (-genes) recognize pathogens and initiate pathogen-specific defense responses. The expression of some -genes carry fitness costs and therefore inducible immune responses are likely advantageous. To what degree inducible resistance driven by -genes is triggered by pathogen infection is currently an open question.

Methods: In this study we analyzed the expression of 940 -genes of tomato and potato across 315 transcriptome libraries to investigate how interspecific interactions with microbes influence -gene expression in plants.

Results: We found that most -genes are expressed at a low level. A small subset of -genes had moderate to high levels of expression and were expressed across many independent libraries, irrespective of infection status. These -genes include members of the class of genes called NRCs (NLR required for cell death). Approximately 10% of all -genes were differentially expressed during infection and this included both up- and down-regulation. One factor associated with the large differences in -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 -gene expression is induced upon pathogen attack. Instead, a small core set of -genes is constitutively expressed, imparting upon the plant a ready-to-detect and defend status.