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

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.

Benzothiadiazole induces disease resistance in Arabidopsis by activation of the systemic acquired resistance signal transduction pathway

“…Associated with the onset of SAR in tobacco is the synthesis of new proteins, some of which are members of the pathogenesis-related (PR) protein gene families. The mRNAs that encode these proteins have been shown to accumulate coordinately in both a temporal and a spatial manner that is consistent with a role for these gene products in SAR (Ward et aL, 1991). In support of this idea, transgenic plants that overexpress various PR genes exhibit enhanced disease resistance Broglie et al, 1991;Liu et al, 1995).…”

Compromising early salicylic acid accumulation delays the hypersensitive response and increases viral dispersal during lesion establishment in TMV‐infected tobacco

“…Recognized genetic markers for the establishment of SAR are the induction of PR protein genes in systemic tissues (Ward et aL, 1991;Yalpani et aL, 1993). Research into the possible systemic signals responsible for initiating acquired resistance has suggested salicylic acid (SA) to be a likely candidate.…”

“…Research into the possible systemic signals responsible for initiating acquired resistance has suggested salicylic acid (SA) to be a likely candidate. Exogenous application of SA induces PR protein gene expression in tobacco (Ward et aL, 1991), cucumber (Metraux et aL, 1990) and Arabidopsis thafiana (Uknes et al, 1993b); whilst endogenous SA levels rise locally around lesions following pathogen attack in tobacco (Malamy et al, 1990;Enyedi et aL, 1992), Arabidopsis thaliana (Uknes et al, 1993b) and also in cucumber, where SA levels were observed to rise in phloem exudates (Metraux et aL, 1990;Rasmussen et al, 1991).…”

Molecular cloning and differential expression of an aldehyde dehydrogenase gene in rice leaves in response to infection by blast fungus

“…SA may act as a key signal molecule in systemic acquired resistance (Ward et al 1991;Ryals et al 1996;Dong 1998;Clarke et al 2000) and induce a series of the systemic acquired resistance-marker proteins. Sano et al (1994) have reported that mechanical wounding induces SA in transgenic tobacco, and wound signals overlap with pathogen signaling pathways.…”