Abstract
Syringolin A, the product of a mixed non-ribosomal peptide/polyketide synthetase, is secreted by Pseudomonas syringae pv. syringae under in planta conditions and is one of the molecular determinants recognized by nonhost plant species. Spray application of syringolin A onto powdery mildew-infected wheat and Arabidopsis has the remarkable effect of reprogramming epidermal cells that are colonized by the powdery mildew fungi Blumeria graminis f. sp. tritici and Erysiphe cichoracearum, respectively, in a compatible interaction to undergo hypersensitive cell death. No hypersensitive cell death is observed if the compound is applied onto uninfected plants. Transcriptome analyses in wheat and Arabidopsis with regard to powdery mildew inoculation and/or syringolin A spraying lead to a hypothesis about how syringolin A may accomplish to induce the hypersensitive reaction (HR) in colonized cells. The model is supported by transcriptome analyis of an Arabidopsis mutant in which HR is not induced upon syringolin A spraying of powdery mildew-infected plants. Cloning of the syringolin A synthetase genes has allowed us to build a detailed model of syringolin A synthesis based on the gene structure. This model in turn enabled us to clone the genes responsible for the synthesis of glidobactins (syn. cepafungins), antibiotics with a structure related to syringolin A that were reported to have antitumor activity, from an unknown species belonging to the order Burkholderiales. Comparisons to the approximately 700 complete eubacterial genomic sequences known resulted in the identification of a small but very intriguing group of pathogenic bacteria postulated to produce glidobacting-like molecules.
Schellenberg, B