Potato homologs of Arabidopsis thaliana genes functional in defense signaling--identification, genetic mapping, and molecular cloning.

Defense against pests and pathogens is a fundamental process controlled by similar molecular mechanisms in all flowering plants. Using Arabidopsis thaliana as a model, steps of the signal transduction pathways that link pathogen recognition to defense activation have been identified and corresponding genes have been characterized. Defense signaling (DS) genes are functional candidates for controlling natural quantitative variation of resistance to plant pathogens. Nineteen Arabidopsis genes operating in defense signaling cascades were selected. Solanaceae EST (expressed sequence tag) databases were employed to identify the closest homologs of potato (Solanum tuberosum). Sixteen novel DS potato homologs were positioned on the molecular maps. Five DS homologs mapped close to known quantitative resistance loci (QRL) against the oomycete Phytophthora infestans causing late blight and the bacterium Erwinia carotovora subsp. atroseptica causing blackleg of stems and tuber soft rot. The five genes are positional candidates for QRL and are highly sequence related to Arabidopsis genes AtSGT1b, AtPAD4, and AtAOS. Full-length complementary DNA and genomic sequences were obtained for potato genes StSGT1, StPAD4, and StEDS1, the latter being a putative interactor of StPAD4. Our results form the basis for further studies on the contributions of these candidate genes to natural variation of potato disease resistance.