Coordinate Gene Activity in Response to Agents That Induce Systemic Acquired Resistance.

TLDR

In plants, necrotic lesions from pathogen infection trigger systemic acquired resistance (SAR), a disease‑resistant state that develops in uninfected tissues after a hypersensitive reaction, as exemplified in tobacco infected with tobacco mosaic virus. The study proposes a model linking pathogen‑induced necrosis to salicylic acid biosynthesis and subsequent SAR induction. The authors found that SAR onset coincides with coordinated induction of nine mRNA classes, and that both salicylic acid and a synthetic immunization compound trigger the same SAR genes, supporting the idea that resistance is driven by coordinated SAR gene expression.

Abstract

In a variety of plant species, the development of necrotic lesions in response to pathogen infection leads to induction of generalized disease resistance in uninfected tissues. A well-studied example of this "immunity" reaction is systemic acquired resistance (SAR) in tobacco. SAR is characterized by the development of a disease-resistant state in plants that have reacted hypersensitively to previous infection by tobacco mosaic virus. Here, we show that the onset of SAR correlates with the coordinate induction of nine classes of mRNAs. Salicylic acid, a candidate for the endogenous signal that activates the resistant state, induces expression of the same "SAR genes." A novel synthetic immunization compound, methyl-2,6-dichloroisonicotinic acid, also induces both resistance and SAR gene expression. These observations are consistent with the hypothesis that induced resistance results at least partially from coordinate expression of these SAR genes. A model is presented that ties pathogen-induced necrosis to the biosynthesis of salicylic acid and the induction of SAR.