Abstract
Plant activators are compounds, such as analogs of the defense hormone salicylic acid (SA), that protect plants from pathogens by activating the plant immune system. Although some plant activators have been widely used in agriculture, the molecular mechanisms of immune induction are largely unknown. Using a newly established high-throughput screening procedure that screens for compounds that specifically potentiate pathogen-activated cell death in Arabidopsis thaliana cultured suspension cells, we identified five compounds that prime the immune response. These compounds enhanced disease resistance against pathogenic Pseudomonas bacteria in Arabidopsis plants. Pretreatments increased the accumulation of endogenous SA, but reduced its metabolite, SA-O-β-d-glucoside. Inducing compounds inhibited two SA glucosyltransferases (SAGTs) in vitro. Double knockout plants that lack both SAGTs consistently exhibited enhanced disease resistance. Our results demonstrate that manipulation of the active free SA pool via SA-inactivating enzymes can be a useful strategy for fortifying plant disease resistance and may identify useful crop protectants.
Highlights
Like animals, plants activate their innate immune system upon recognition of pathogens
We found that active compounds inhibit both a known and a previously unknown salicylic acid (SA) glucosyltransferase (SAGT)
We expected that immunepriming chemicals would increase plants infected with the virulent strain (Pst)-avrRpm1–induced cell death, but cells that were not exposed to the pathogen should not show any effects
Summary
Plants activate their innate immune system upon recognition of pathogens. Pathogen-associated molecular patterns or pathogen effectors are recognized by either transmembranetype pattern recognition receptors or cytosolic nucleotide binding and Leu-rich receptors and trigger a range of defense responses (Dangl and Jones, 2001). The SA regulatory mechanisms may be exploited for developing crop protection technologies through molecular breeding or chemical applications. Applied SA stimulates defense responses and confers disease resistance in plants. A number of chemicals that mimic SA action have been developed. These compounds are commonly called plant activators, and various types of compounds have been examined (Kessmann et al, 1994; Schreiber and Desveaux, 2008).
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