Characterization of a novel Toll/interleukin-1 receptor (TIR)-TIR gene differentially expressed in common bean (Phaseolus vulgaris cv. Othello) undergoing a defence response to the geminivirus Bean dwarf mosaic virus

SUMMARY Common bean (Phaseolus vulgaris L.) cultivar (cv.) Othello develops a hypersensitive response-associated vascular resistance to infection by Bean dwarf mosaic virus (BDMV), a single-stranded DNA virus (genus Begomovirus, family Geminiviridae). A PCR-based cDNA subtraction approach was used to identify genes involved in this resistance response. Eighteen clones, potentially involved with BDMV resistance, were identified based upon being up-regulated in BDMV-infected tissues and/or having sequence similarity with known resistance-associated genes. Analysis of these clones revealed potential genes involved in pathogen defence, including pathogenesis-related protein genes and resistance gene analogues (RGAs). Further characterization of one RGA, F1-10, revealed that it encodes a predicted protein with a double Toll/interleukin-1 receptor (TIR) motif. Full-length (F1-10) and spliced (F1-10sp) forms of the RGA were strongly up-regulated in BDMV-infected cv. Othello hypocotyl tissues by 4 days post-inoculation, but not in equivalent mock-inoculated tissues. In agroinfiltration experiments, F1-10, but not F1-10sp, mediated resistance to BDMV in the susceptible common bean cv. Topcrop. By contrast, transgenic Nicotiana benthamiana lines expressing F1-10 or F1-10sp were not resistant to BDMV. Interestingly, when these transgenic lines were inoculated with the potyvirus Bean yellow mosaic virus, some F1-10 lines showed a more severe symptom phenotype compared with non-transgenic control plants. Based on these findings, F1-10 was named: Phaseolus vulgaris VIRUS response TIR-TIR GENE 1 (PvVTT1).