Constitutively Expressed RB Gene Confers a High Level but Unregulated Resistance to Potato Late Blight

Abstract

The RB gene, which was cloned from the wild potato species Solanum bulbocastanum, confers a high level of broad spectrum resistance to various strains of Phytophthora infestans, the causal agent of potato late blight. The level of RB-mediated resistance is correlated with the amount of RB transcripts in transgenic potato lines containing RB gene(s) driven by its native promoter. To assess whether the level of RB-mediated resistance can be further enhanced by overexpression of the RB gene, multiple transgenic potato lines containing RB gene(s) driven by the cauliflower mosaic virus (CaMV) 35S promoter were developed. Surprisingly, all 35S::RB transgenic lines with one or several copies of the RB gene showed a similar level of late blight resistance. In parallel, a statistically similar amount of RB transcript was observed among all resistant transgenic lines with different copy numbers of the RB gene. In addition, the levels of RB gene transcription in the 35S::RB transgenic potato lines were the same or lower than in transgenic lines containing the RB gene driven by its native promoter. Thus, developing transgenic potato lines using RB with the native promoter will be the best approach to deploy this gene for combating late blight.