Developmental and pathogen-induced accumulation of transcripts of polygalacturonase-inhibiting protein in Phaseolus vulgaris L.

Abstract.

Expression of the polygalacturonase-inhibiting-protein gene ( pgip) during development of French bean (Phaseolus vulgaris L. cv. Red Kidney) was analysed in various organs, including leaves, stems and roots of etiolated and light-grown seedlings, light-grown adult plants, as well as flowers, pods, and seeds. In light-grown seedlings and plants, pgip transcripts were detected in all tissues examined, with higher levels found in the transition zone between the elongating and mature region of young hypocotyls, and in the basal region of the stem of adult plants. In etiolated hypocotyls, levels of pgip transcripts in the elongating region were five- to six fold higher than in light-grown hypocotyls. High levels of transcripts were also observed in pods. Accumulation of pgip mRNA was also followed in both compatible and incompatible race-cultivar interactions between Colletotrichum lindemuthianum races α and γ, respectively, and P. vulgaris by Northern blot analysis and in situ hybridisation. In situ experiments showed, in incompatible interactions, a rapid, intense and transient accumulation of pgip mRNA in epidermal cells proximal to the site of infection, and, less intense, within the cortical parenchyma underneath. In compatible interactions, no substantial accumulation of pgip mRNA was observed in hypocotyls; a very weak accumulation was observed in leaves during lesion formation.