Higher Copy Numbers of the Potato RB Transgene Correspond to Enhanced Transcript and Late Blight Resistance Levels

Abstract

Late blight of potato ranks among the costliest of crop diseases worldwide. Host resistance offers the best means for controlling late blight, but previously deployed single resistance genes have been short-lived in their effectiveness. The foliar blight resistance gene RB, previously cloned from the wild potato Solanum bulbocastanum, has proven effective in greenhouse tests of transgenic cultivated potato. In this study, we examined the effects of the RB transgene on foliar late blight resistance in transgenic cultivated potato under field production conditions. In a two-year replicated trial, the RB transgene, under the control of its endogenous promoter, provided effective disease resistance in various genetic backgrounds, including commercially prominent potato cultivars, without fungicides. RB copy numbers and transcript levels were estimated with transgene-specific assays. Disease resistance was enhanced as copy numbers and transcript levels increased. The RB gene, like many other disease resistance genes, is constitutively transcribed at low levels. Transgenic potato lines with an estimated 15 copies of the RB transgene maintain high RB transcript levels and were ranked among the most resistant of 57 lines tested. We conclude that even in these ultra-high copy number lines, innate RNA silencing mechanisms have not been fully activated. Our findings suggest resistance-gene transcript levels may have to surpass a threshold before triggering RNA silencing. Strategies for the deployment of RB are discussed in light of the current research.

The Effect of Growth Regulators and a Biostimulator on the Health Status, Yield and Yield Components of Potatoes (Solanum tuberosum L.)

“…Late blight (Phytophthora infestans) is the most devastating disease in potato farms during the growing season (Fry 2008;Bradeen et al 2009;Chmielarz et al 2014;Mosquera et al 2016). Under favorable conditions, the pathogen can significantly lower yields, and late blight epidemics can result in the destruction of entire harvests.…”

Identification, Mapping and Pyramiding of Genes/Quantitative Trait Loci (QTLs) for Durable Resistance of Crops to Biotic Stresses

“…Thus, recently molecular markers and genetic engineering are widely used in crop improvement program to stack series of resistance genes into elite cultivar to develop durable and/or broad-spectrum resistance to biotic stress. Therefore, to minimize yield loss due to biotic stress, developing countries including Ethiopia shall include gene pyramiding in their Late blight R genes from wild relatives Foster et al [113] Late blight R gene from wild relative Bradeen et al [114] Late blight R gene from wild relative Halterman et al [115] Potato virus X Mammalian interferoninduced enzyme Truve et al [116] Rice Bacterial blight and bacterial streak Engineered E gene Hummel et al [30] Bacterial streak R gene from maize Zhao et al [117] Squash …”

R/Avr gene expression study of Rpi-vnt1.1 transgenic potato resistant to the Phytophthora infestans clonal lineage EC-1

“…Due to the low level of expression of Avr-vnt1 or for technical reasons, Pel (2010) could not establish such a relationship for Rpi-vnt1.1, as was also reported by Stefańczyk et al (2017) and by us in this study. Rpi-vnt1.1 transcript level may be higher when the gene is in a highly transcriptionally active region of the genome, or if the gene is present in numerous copies (Bradeen et al 2009). Indeed, our observation that the disease scores vary continuously from fully susceptible to highly resistance for the 52 transgenic events tested is likely related to the amount of Rpivnt1.1 transcripts which could be gene expression (positional effect) and/or number of copies of the Rpi-vnt1.1 gene.…”