Pathogenesis-Related Acidic Β-1,3–Glucanase Genes of Tobacco Are Regulated by Both Stress and Developmental Signals. François Côté. Départment de Phytologie, Faculté des Sciences de l’Agriculture et de l’Alimentation, Université Laval, Sainte-Foy, Québec, Canada G1K 7P4. John R. Cutt(2), Alain Asselin(1), and Daniel F. Klessig(2). (1)Départment of Phytologie, Faculté des Sciences de l’Agriculture et de l’Alimentation, Université Laval, Sainte-Foy, Québec, Canada G1K 7P4, and (2)Waksman Institute, Rutgers The State University of New Jersey, Piscataway 08855-0759, U.S.A. MPMI 4:173-181. Accepted 13 December 1990. Copyright 1991 The American Phytopathological Society.

Three pathogenesis-related (PR) proteins of tobacco are acidic isoforms of Β-1,3-glucanase (PR-2a, -2b, -2c). We have cloned and sequenced a partial cDNA clone (λFJ1) corresponding to one of the PR-2 Β-1,3-glucanases. A small gene family encodes the PR-2 proteins in tobacco, and similar genes are present in a number of plant species. We analyzed the stress and developmental regulation of the tobacco PR-2 Β-1,3-glucanases by using northern and western analyses and a new technique to assay enzymatic activity. Stress caused by both thiamine and tobacco mosaic virus (TMV) infection resulted in a dramatic increase in the levels of PR-2 mRNA, protein, and enzyme activities. The increased PR-2 gene expression in upper uninoculated leaves of plants infected with TMV also suggests a role in systemic acquired resistance. During floral development, a number of Β-1,3-glucanase activities were observed in all flower tissues. However, PR-2 polypeptides were observed only in sepal tissue. In contrast, an mRNA that hybridized to the PR-2 cDNA was present in stigma/style tissue and the sepals. Primer extension analysis confirmed the identity of the PR-2 mRNA in sepals, but indicated that the Β-1,3-glucanase gene expressed in the stigma/style of flowers was distinct from the PR-2 genes. The induction of PR-2 protein synthesis by both stress and developmental signals was accompanied by a corresponding increase in the steady-state levels of PR-2 mRNA, suggesting that PR-2 gene expression is regulated, in part, at the level of mRNA accumulation.