The effect of sense and antisense expression of the PR-N gene for beta-1,3-glucanase on disease resistance of tobacco to fungi and viruses

Constitutive expression of a beta-1,3-glucanase cDNA coding for the PR-N isoform in tobacco plants increased resistance of the foliage of T2 progenies of transgenic regenerated lines to the glucan-containing fungi Peronospora tabacina and Phytophthora parasitica var. nicotiana. Resistance was not observed when the T2 progenies were challenged with tobacco mosaic virus, tobacco etch virus or tobacco vein mottling virus. Such plants had higher levels of beta-1,3-glucanase activity than the controls. Gel electrophoresis showed the presence of a glucanase band that migrated in the same position as the isoform PR-N in three sense regenerated transgenic lines. Resistance to P. tabacina and P. parasitica var. nicotiana in the leaves was closely associated with high levels of beta-1,3-glucanase activity. Introduction of the antisense cDNA in one of the antisense regenerated lines was associated with lower levels of beta-1,3-glucanase activity and decreased resistance to P. tabacina and P. parasitica var. nicotiana in its progenies after induction with TMV. No increase in susceptibility against any of the viruses tested was observed in the T2 progenies of the antisense Lines after induction. At 7 days after challenge with P. tabacina, all plants had high levels of beta-1,3-glucanase activity and the same PR-protein pattern. These results suggest that the beta-1,3-glucanase isoform N is important for resistance of tobacco plants against the fungi tested but not against viruses. (C) 1996 Academic Press Limited.