N-acetylchitooligosaccharides elicit expression of a single (1→3)-β-glucanase gene in suspension-cultured from barley (Hordeum vulgare)

Abstract

N-acetylchitooligosaccharides of degree of polymerization 6 to 8 elicit the synthesis of (1→3)-β-glucan endohydrolase (EC 3.2.1.39) activity in suspension-cultured cells derived from immature barley (Hordeum vulgare) embryos. Corresponding de-acety-lated chitooligosaccharides have no effect. Concentrations of N-acetylchitoheptaose in the 200 nM range are sufficient to elicit the response. A 2- to 3-fold increase in (1→3)-β-glucanase activity is detected 24 h after the addition of the oligosaccharide. Non-denaturing gel electrophoresis, coupled with the in situ detection of (1→3)-β-glucanase activity in the gels, has enabled the separation of specific isoforms of the enzyme. The increase in (1→3)-β-glucanase activity following N-acetylchitoheptaose induction is attributable predominantly to enhanced levels of isoenzyme GII, although the barley (1→3)-β-glucanase gene family encodes at least seven different isoforms of the enzyme. Northern hybridization analyses with gene-specific probes confirmed the presence of mRNA encoding isoenzyme GII as the major mRNA in cells treated with the oligosaccharide elicitor. The results therefore demonstrate a specific induction of the (1→3)-β-glucanase isoenzyme GII gene following stimulation of barley cells with oligosaccharides of fungal cell wall origin, and further suggest that a plant's response to microbial attack involves transcription of quite specific members of the gene families that encode pathogenesis-related proteins.