Does Foliar Blight Resistance
R Gene RB Function For Tuber Blight Control? Millett, B.P. and J.M. Bradeen
Plant & Animal Genome
XIII (
The NBS-LRR genes, composing the largest class of cloned
plant R genes, are presumed to be constitutively expressed in all plant tissues
so that pathogens are readily detected. The differential expression of the
NBS-LRR gene, RB, provides an interesting model for investigating this
class of genes. RB, which was recently cloned from the wild potato species
Solanum bulbocastanum, imparts broad-spectrum foliar blight resistance
to all known races of Phytophthora infestans, the causal organism of
late blight. Since both foliage and tubers are natural targets of P.
infestans, it is easy to comprehend why late blight is responsible for
multibillion dollar losses worldwide annually. Using RT-PCR, we have observed
that while RB (under its own promoter) is expressed in leaves of both
transgenic cultivated potato and its native S. bulbocastanum, the gene
behaves differently in tubers: RB is expressed in transgenic tubers but
not in S. bulbocastanum tubers. Whole tuber and tuber slice assays of S.
bulbocastanum and transgenic cultivated potato provide a phenotypic
comparison to the genotypic data. On-going foliar and tuber assays continue to
provide a more complete picture of the behavior of the R gene RB.