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 ).