Structure and expression of a barley acidic ?-glucanase gene

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Abstract
A barley acidic β-1,3-glucanase gene was recovered from a barley genomic library by homology with a partial cDNA of barley basic β-1,3-glucanase isoenzyme GII. The gene, Abg2, is homologous to the PR2 family of pathogenesis-related β-1,3-glucanase genes. The ABG2 protein has 81% amino acid similarity to barley basic β-1,3-glucanase GII. The ABG2 protein is encoded as a preprotein of 336 amino acids including a 28 amino acid signal peptide. A 299 bp intron occurs within codon 25. The mature ABG2 protein has a predicted mass of 32642 Da and a calculated isoelectric point of 4.9. The second exon of the Abg2 gene shows a strong preference for G+C in the third position of degenerate codons. The Abg2 gene was functionally expressed in Escherichia coli. Abg2 mRNA is constitutively expressed in barley root; leaf expression of Abg2 mRNA is induced by mercuric chloride and infection by Erysiphe graminis f. sp. hordei. Southern blot analysis indicates that Abg2 is a member of a small gene family.