Xylanase, a Novel Elicitor of Pathogenesis-Related Proteins in Tobacco, Uses a Non-Ethylene Pathway for Induction

Abstract

Antisera to acidic isoforms of pathogenesis-related proteins were used to measure the induction of these proteins in tobacco (Nicotiana tabacum) leaves. Endo-(1-4)-i-xylanase purified from culture filtrates of Trichoderma viride was a strong elicitor of pathogenesis-related protein synthesis in tobacco leaves. The synthesis of these proteins was localized to tissue at the area of enzyme application. The inhibitors of ethylene biosynthesis and ethylene action, 1-aminoethoxyvinylglycine and silver thiosulfate, inhibited accumulation of pathogenesis-related proteins induced by tobacco mosaic virus and a-aminobutyric acid, but did not inhibit elicitation by xylanase. Likewise, the induction of these proteins by the tobacco pathogen Pseudomonas syringae pv. tabaci was not affected by the inhibitors of ethylene biosynthesis and action. The leaf response to tobacco mosaic virus and aaminobutyric acid was dependent on light in normal and photosynthetically incompetent leaves. In contrast, the response of leaves to xylanase was independent of light. Tobacco mosaic virus and a-aminobutyric acid induced concerted accumulation of pathogenesis-related proteins. However, xylanase elicited the accumulation of only a subset of these proteins. Specifically, the plant (1-3)-,6-glucanases, which are normally a part of the concerted response, were underrepresented. These experiments have revealed the presence of a novel ethylene-independent pathway for pathogenesis-related protein induction that is activated by xylanase.The de novo synthesis of PR2 proteins is a ubiquitous reaction of monocot (10,23,33)

UV-B-Induced PR-1 Accumulation Is Mediated by Active Oxygen Species.

“…The higher basal level detected in control albino leaves was reported previously (Lotan and Fluhr, 1990). Thus, it appears that ROS involved in the signal transduction pathway between UV-B and PR-1 are not generated during photosynthesis.…”

“…UV-B appeared to be a potent inducer, consistently inducing equal or higher levels of acidictype PR-1 protein synthesis than a-aminobutyric acid, which itself has been reported to be an effective elicitor of PR-1 protein induction (Lotan and Fluhr, 1990). Irradiation with UV-A (320 to 360 nm) did not cause induction of PR-1 protein, suggesting that this response is specific to the shorter wavelengths of UV.…”

“…These proteins have been shown to be induced in response to a variety of stimuli, including funga1 and bacterial infection and exogenously applied elicitors, such as salicylic acid (SA), ethylene, and xylanase (Asselin et al, 1985;BOI et al, 1990;Lotan and Fluhr, 1990;Eyal et al, 1992). In addition, irradiation with the shorter wavelength, UV-C (200 to 280 nm), has been previously shown to cause induction of all PR protein families (Brederode et al, 1991).…”

Calcium Requirement for Ethylene-Dependent Responses.

“…One pathway is ethylene dependent and is exemplified by ethylene itself (Boller et al, 1983;Ecker and Davis, 1987). It also includes elicitors, such as a-aminobutyric acid (a-AB), that promote ethylene production and require ethylene in their mode of action (Lotan and Fluhr, 1990b;Eyal and Fluhr, 1992). The other pathway is ethylene independent (Mauch et al, 1984) and is exemplified by the fungal endoxylanase.…”

“…The enzyme apparently degrades P-1,4-xylan linkages in the plant cell wall and is an exceptionally potent inducer of chitinase accumulation. It also promotes ethylene evolution (Fuchs et al, 1989); nevertheless, ethylene is not required in its mode of action (Lotan and Fluhr, 1990b).…”