Tissue-specific expression of a late blight R gene in wild and cultivated potato species Millett, B.P. and J.M. Bradeen

American Phytopathological Society Annual Meeting (Anaheim, CA Aug 2004)

The NBS-LRR class of resistance I genes accounts for 75% of cloned plant R genes. These genes encode sentinels that are involved in pathogen detection and defense response initiation. As sentinels, R genes are presumed to be constitutively expressed in all plant tissues, even in the absence of the pathogen. The NBS-LRR R gene, RB, recently cloned from the wild potato species Solanum bulbocastanum imparts resistance to Phytophthora infestans, the causal organism of Late Blight, a disease responsible for multibillion dollar losses worldwide. Potato late blight tuber resistance is just as essential as foliar resistance since these two distinct tissues are both natural targets of P. infestans. Here, we examined RB expression using RT-PCR and compared expression in leaves and tubers. In S. bulbocastanum, we found that RB is constitutively expressed in leaves, but apparently not expressed at all in the tuber. We are currently examining RB expression in transgenic cultivated potato. The lack of expression of RB in the tuber could explain why tubers of foliar resistant potato plants are still susceptible to P. infestans.