Dark-induced accumulation of a basic pathogenesis-related (PR-1) transcript and a light requirement for its induction by ethylene.

A gene encoding a basic-type pathogenesis-related protein from Nicotiana tabacum (prb-1b) was cloned, sequenced and characterized. It contains an open reading frame of 179 amino acids that is ca. 65% homologous with the acidic PR-1 class of pathogenesis-related proteins and 87% homologous with a different basic-type PR-1 gene. In the light, physiological levels of ethylene rapidly (1 h) induced basic, but not acidic-type, PR-1 transcript. Additional elicitors acting via ethylene, such as alpha-aminobutyric acid, were shown to induce basic- and acidic-type PR-1 transcript accumulation in a light-dependent manner. In contrast, xylanase, an ethylene-independent elicitor, induced transcript accumulation of basic- and acidic-type PR-1 in a light-independent manner. Dark-induced accumulation of basic PR-1 transcript occurred at night in greenhouse-grown plants and, to a greater extent, in continuously dark-treated plants. The novel dark regulation may point to additional nonpathogenesis-related roles for these genes in plant-environment interactions.