ANALYSIS OF GENE FAMILIES ENCODING ACIDIC AND BASIC BETA-1,3-GLUCANASES OF TOBACCO

Healthy tobacco plants accumulate β-1,3-glucanases (glucan endo-1,3-β-glucosidase; EC 3.2.1.39) in their roots and in specific parts of the flowers. After infection with tobacco mosaic virus, acidic and basic β-1,3-glucanases are induced in the inoculated and virus-free leaves of the plant. An analysis of cDNA clones demonstrated that at least five genes for acidic β-1,3-glucanases are induced after tobacco mosaic virus infection. Southern blot analysis indicated that the tobacco genome contains approximately eight genes for acidic β-1,3-glucanases and a smaller number of genes encoding basic β-1,3-glucanases. Genes from both gene families were cloned and sequenced. The basic isozymes contain a C-terminal extension that is cleaved off during their targeting to the vacuoles. This extension is absent in the acidic isozymes, which accumulate extracellularly. Northern blot hybridization showed that genes encoding acidic and basic β-1,3-glucanases are strongly induced after tobacco mosaic virus infection or salicylate treatment of tobacco. The cloning of these genes is a first step toward the identification of regulatory elements involved in their coordinate induction.