The small molecule 2-furylacrylic acid inhibits auxin-mediated responses in Arabidopsis thaliana

Auxins, typified by IAA, are a class of plant hormones involved in a wide array of processes including cell division, cell elongation, tissue patterning, phototropism, gravitropism and root development. Despite recent descriptions of the machinery involved in auxin transport and perception, additional regulatory mechanisms and components remain to be identified and characterized. Chemical genetics has proven to be a valuable means by which to investigate the auxin response pathway in Arabidopsis thaliana. A screen for small molecules that block auxin signaling was performed previously, leading to the characterization of four compounds with this inhibitory activity. Here, we have synthesized various analogs of one of these molecules, compound A, a furyl acrylate ester of a thiadiazole heterocycle. The biological activity of these derivatives was initially assessed based on their ability to inhibit the auxin-inducible expression of the BA3-GUS reporter gene and indicated that the active portion of the molecule was 2-furylacrylic acid (2-FAA). In the micromolar range, 2-FAA attenuates the auxin-inducible expression of IAA5, fails to alter the interaction of IAA7/AXR2 with the SCFTIR1 complex and inhibits both root and hypocotyl elongation of wild-type seedlings. Based on our structure-function analysis of compound A, we conclude that 2-furylacrylic acid is liberated by hydrolysis of an ester linkage. Identification of the cellular target of this molecule will add to our understanding of auxin-mediated events.