Transcriptional studies of the late blight resistance gene RB in foliage of transgenic potato

Massimo Iorizzo^1,2, Dimitre S. Mollov¹, Benjamin P. Millett¹, Domenico Carputo², and James M. Bradeen¹

¹University of Minnesota, Department of Plant Pathology, 495 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108 USA

²University of Naples “Federico II”, Department of Soil, Plant, Environmental, and Animal Production Sciences, Via Università 100, 80055 Portici (NA) Italy

Late blight, caused by the oomycete pathogen Phytophthora infestans, is the most devastating potato disease in the world. The resistance gene RB imparts broad-spectrum foliar blight resistance to transgenic cultivated potato. This project evaluates RB transcription in the foliage of transgenic potato under standard field conditions, variable temperatures, and at different stages of physiological development. An RT-PCR assay specific for the RB transgene was developed and adapted for real time quantification. In total, 57 transgenic (+RB) lines from four different potato cultivars were evaluated in replicated field tests for foliar blight resistance to P. infestans US8. Transgenic lines were divided into susceptible, moderately susceptible, moderately resistant, and resistant categories. Results confirm a positive correlation between RB transcript levels and field resistance. This implies that foliar resistance may be enhanced by augmenting RB transgene transcription, which will be explored in future studies. In a second set of experiments, transgenic potatoes were grown in growth chambers at varying temperatures (10°C, 20°C, and 30°C). RB transcript was detected at all temperatures, suggesting the transgene is transcribed under a wide range of environmental conditions. Finally, in greenhouse assays, foliar resistance was evaluated in transgenic plants at three physiological stages (pre-flowering, barely post-flowering, and post-flowering). Disease resistance declined as plants aged, consistent with a general trend for late blight resistance previously noted in potato. Paired real time RT-PCRs are ongoing.