The structure, genomic organization, and temporal pattern of activation of a gene encoding a pathogenesis-related protein (PR1) in potato (Solanum tuberosum) have been analyzed. The gene is rapidly activated in leaves from the potato cultivar Datura, containing the resistance gene R1, in both compatible and incompatible interactions with appropriate races of the late-blight fungus Phytophthora infestans. Activation is also observed in leaves treated with fungal elicitor. The gene occurs in multiple, very similar copies and encodes a polypeptide (Mr = 25,054; pI = 5.5) that is classified as a PR protein by several criteria. Small fragments with great sequence similarity to portions of the two exons were found closely linked to the expressed gene, which altogether represents a simple case of genome organization in potato. The coding sequence of the prp1 gene and the deduced amino acid sequence are strikingly similar to the corresponding sequences of a 26-kDa heat shock protein from soybean.

Transcription of at least one member of the potato prp1 gene family, prp1-1, is activated at early stages of potato infection with the late blight fungus Phytophthora infestans. In this paper we present evidence that mRNA encoded by prp1-1 does not accumulate in response to abiotic environmental cues which stimulate transcription of other defence-related genes. Regulatory elements were identified in the 5' terminal region of prp1-1 by assaying the expression pattern of chimeric promoter/beta-glucuronidase gene constructs in transgenic potato. A 273 bp fragment comprising the promoter sequence between positions -402 and -130 was sufficient for rapid and strictly localized transcriptional activation at infection sites during the development of late blight disease. Like the native promoter, this truncated promoter did not mediate transcriptional activation in response to other abiotic stimuli. The use of the identified regulatory region to generate conditional mutations selectively at infection sites is discussed.