Abstract
Salicylic acid (SA) is an essential hormone for development and induced defense against biotrophic pathogens in plants. The formation of SA mainly derives from chorismate via demonstrated isochorismate synthase (ICS) and presumed isochorismate pyruvate lyase (IPL)-mediated steps in Arabidopsis thaliana, but so far no plant enzyme displaying IPL activity has been identified. Here, we developed an E. coli SA biosensor to screen for IPL activity based on the SalR regulator/salA promoter combination from Acinetobacter sp ADP1, to control the expression of the reporter luxCDABE. The biosensor was responsive to micromolar concentrations of exogenous SA, and to endogenous SA produced after transformation with a plasmid permitting IPTG-inducible expression of bacterial IPL in this biosensor strain. After screening a cDNA library constructed from turnip crinkle virus (TCV)-infected Arabidopsis ecotype Di-17, we identified an enzyme, PRXR1, as a putative IPL that converts isochorismate into SA. Our results provide a new experimental approach to identify IPL and new insights into the SA biosynthesis pathway in Arabidopsis.
Highlights
Salicylic acid (SA) is a small phenolic compound present in plants and bacteria
XL1-LUX exhibited increased luciferase expression for concentrations of salicylate between 0 and 500 μM when the cells were grown in liquid medium at room temperature (22 °C) and 28 °C with fourfold and fivefold increased luminescence compared to uninduced cells (Fig. 1c)
When grown on solid medium at room temperature, luminescence responded likewise to increasing SA concentrations (Fig. 1d). These results indicated that the XL1-LUX biosensor was capable of detecting exogenous SA with a useful dose–response relationship at lower growth temperatures
Summary
Salicylic acid (SA) is a small phenolic compound present in plants and bacteria. SA is an essential signaling molecule that mediates defense against infections with biotrophic pathogens and is produced to regulate several physiological functions, including flowering induction and seed germination (Rivas-San Vicente and Plasencia 2011; Spoel and Dong 2012). SA functions as a precursor of siderophores in many bacteria, such as pyochelin in Pseudomonas aeruginosa, yersiniabactin in Yersinia pestis and Y. enterocolitica, and mycobactin in Mycobacterium tuberculosis (Cox et al 1981; Crosa and Walsh 2002; Gaille et al 2003; Pelludat and Brem 2003).
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