N‐acetylchitooligosaccharides elicit expression of a single (1→3)‐β‐glucanase gene in suspension‐cultured cells 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 ofN‐acetylchitoheptaose in the 200 nMrange 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 followingN‐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.