Gene structure and a possible cytoplasmic location for (1(r)3)-b-glucanase isoenzyme GI from barley (Hordeum vulgare)

Abstract

A genomic DNA fragment encoding (1 → 3)-β-glucan endohydrolase (EC 3.2.1.39) isoenzyme GI from barley has been isolated and characterized. The gene has clearly identifiable promoter sequences and a characteristic bias in codon usage but, in contrast to other barley (1 → 3)-β-glucanase genes, has no introns. The amino acid sequence derived from the nucleotide sequence indicates that, unlike other plant pathogenesis-related proteins, the nascent enzyme has no vacuolar or endoplasmic reticulum targeting signals, or any other obvious sequence motifs that have been implicated in intracellular transport. This suggests that the enzyme may be located in the cytosol. Tissue extractions coupled with non-denaturing gel electrophoresis confirmed that the barley (1 → 3)-β-glucanase isoenzyme GI has an intracellular location in young leaves. Members of the barley (1 → 3)-β-glucanase family are now known to be distributed in the cytosol, the vacuole and the extracellular space, and this provides functional opportunities tO inhibit the advance of pathogenic fungi at several levels.