STIGMA-SPECIFIC AND VASCULAR-SPECIFIC EXPRESSION OF THE PR-10A GENE OF POTATO - A NOVEL PATTERN OF EXPRESSION OF A PATHOGENESIS-RELATED GENE

The tissue- and organ-specific expression of PR-10a (formerly STH-2), a pathogenesis-related gene of potato, was investigated using an anti- PR-10a antibody and transgenic potato plants transformed with PR-10a p romoter-beta-glucuronidase (GUS) chimeric gene, Strong PR-10a expressi on was observed in tubers, stolons, stems, and petioles following infe ction with the potato pathogen Phytophthora infestans or elicitation w ith P infestans homogenate, These tissues also responded to different degrees to wounding, Induction in leaves was weak and detectable only with the elicitor treatment, Histochemical GUS staining indicated that PR-10a induction was associated with vascular bundles, Tuber storage parenchyma responded locally to wounding and infection but to a much s maller extent than vascular bundles, In infected petioles and stems, G US activity was seen in most cell types beneath the infection site, wi th strongest expression in vascular cells, PR-10a expression was very vascular-specific in wounded stems and petioles, as well as in elicito r-treated leaves. In healthy, unstressed plants, PR-10a was expressed exclusively in the stigma, Neither GUS activity nor PR-10a protein was detected in vegetative shoot tissues, or in style, ovary, sepal, peta l, or anther extracts, The stigma-specific expression was shown to be developmentally regulated, with more PR-10a protein accumulating in th e stigmas of fully open than unopened flowers, Histochemical GUS stain ing indicated strongest PR-10a expression in the papillae and uppermos t cell layers of the stigma, with lower levels of expression in cell l ayers below, Although the general pattern of expression of PR-10a rese mbles the pattern of expression of genes encoding cell wall protein ge nes, its organ- and tissue-specific expression differentiates it from most other defense-related proteins and genes, This suggests that PR-1 0a plays a unique role in plant defense.