Synthesis and localization of pathogenesis-related proteins in tobacco.

Abstract

The PR1 family of pathogenesis-related proteins from tobacco (Nicotiana tabacum L.) leaves is induced by a variety of pathogenic and chemical agents and is associated with resistance to tobacco mosaic virus. The majority of the PR1 proteins did not copurify with mesophyll protoplasts (the major cell type of the leaf) isolated from tobacco mosaic virus-infected N. tabacum cv. Xanthi-nc leaves. However, these isolated protoplasts were capable of synthesizing and selectively secreting the PR1 proteins. Using monoclonal antibodies for immunofluorescence microscopy, we localized these proteins to the extracellular spaces predominantly in regions adjacent to viral lesions as well as in xylem elements of infected leaves.Infection of tobacco leaves with tobacco mosaic virus (TMV) results in one of two distinct disease processes that depend upon both the genetic background of the host and the viral strain involved. Many tobacco cultivars undergo a "systemic" infection in which TMV spreads from the original point of entry to many parts of the host with the potential of causing widespread damage, especially in younger leaves. In contrast, some tobacco cultivars are able to restrict (localize) the spread of TMV to a small zone of tissue around the point of entry where a necrotic lesion later appears. In tobacco, this "hypersensitive" reaction is accompanied by the induction throughout the plant of acquired resistance: the appearance of smaller and often fewer necrotic lesions in response to a second exposure to TMV (16,17). Virus localization and the induction of acquired resistance are accompanied by the synthesis of abundant amounts of pathogenesis-related (PR) proteins. The production of these proteins may be part of a general defense mechanism against pathogenic attack, since their synthesis can also be induced by certain bacteria and fungi (9,19). Alternatively, their induction by a number of chemical agents, such as acetylsalicylic acid (20), suggests that they are synthesized by the plant in response to stress.The polypeptides of the PR1 gene family, PRla, PRlb, and PRlc, with molecular weights of approximately 15,000, are biochemically and genetically the best characterized PR proteins (1,3,6,13). Their synthesis is regulated predominantly at the level of mRNA accumulation and occurs on membrane-bound polysomes (5, 6, 11). The observation that these proteins can be extracted from TMV-infected leaves by vacuum infiltration suggests that they accumulate in the intercellular fluid of leaves (15) infected whole leaf tissue or from mesophyl protoplasts prepared from this tissue were subjected to immunoblot analysis with a combination of polyclonal rabbit antisera against PR1 and the large subunit (LSU) of ribulose-1,5-bisphosphate carboxylase. Although the LSU was enriched in the mesophyll protoplast preparation as expected, less than 20% of the PR1 proteins found in the whole leaf preparation copurified with the mesophyll protoplasts (Fig. 1). Similar results were obtained with mesophyll protoplasts isolated from leave...

Sunflower (Helianthus annuus L.) Pathogenesis-Related Proteins (Induction by Aspirin (Acetylsalicylic Acid) and Characterization)

“…Acidic isoforms are located in the extracellular spaces of the tissues, whereas basic isoforms are intracellular and found in the vacuoles (Carr et al, 1987;Van Den Bulcke et al, 1989;Grosset et al, 1990;Keefe et al, 1990). The situation is less well defined for other plant species, and basic PR protein isoforms, such as basic chitinases and 0-1,3-glucanases, have also been detected in the extracellular spaces of potato (Kombrink et al, 1988).…”

Cyanide Restores N Gene–Mediated Resistance to Tobacco Mosaic Virus in Transgenic Tobacco Expressing Salicylic Acid Hydroxylase

“…Soluble proteins were extracted and subjected to protein gel blot analysis by using polyclonal rabbit antisera raised against the TMV coat protein (CP) and the tobacco PR-1 protein, using previously described methods (Carr et al, 1987;Carr and Zaitlin, 1991). Purification of total single-stranded RNA was performed using the method of Berry et al (1985), and RNA gel blot analysis of TMV-specific RNAs N gene-mediated recognition of TMV results from the interaction of the N gene product (Whitham et al, 1994) with sequences of the 126-kD replicase protein of TMV (Padgett et al, 1997).…”

Virulence of the Phytopathogen Pseudomonas syringae pv. Maculicola Is rpoN Dependent

“…The HR is accompanied by the induction of defense-related genes (7,91) that are differentially expressed depending on the particular pair of avr and R gene products eliciting the HR (70,72). Defense gene induction also occurs in the absence of the HR during compatible pathogen-host interactions, although usually later and at lower levels than those occurring during an HR (11,32,66).…”