Salicylic acid-independent induction of pathogenesis-related gene expression by fusicoccin

Abstract.

 Treatment of tomato plants (Lycopersicon esculentum Mill.) with fusicoccin (FC), an activator of the plasma-membrane H⁺-ATPase which maintains an electrochemical gradient across the plasma membrane, resulted in a dose-dependent accumulation of transcripts for intra- and extracellular pathogenesis-related (PR) proteins. The accumulation of PR protein transcripts was paralleled by an increase in leaf salicylic acid (SA) content. Transcripts of PR proteins and SA started to accumulate 3 h after FC treatment. 2-Aminoindan-2-phosphonic acid, an inhibitor of SA synthesis, was used to assess the role of SA in FC-mediated induction of PR gene expression. 2-Aminoindan-2-phosphonic acid was found to suppress the accumulation of SA but not the induction of PR gene expression in response to FC treatment. Furthermore, in transgenic tobacco plants overexpressing a bacterial salicylate hydroxylase gene (nahG-tobacco), PR transcripts accumulated after FC treatment to levels similar to those observed in control tobacco plants. The data indicate a role for the proton gradient across the plasma membrane in the SA-independent induction of PR gene expression.