Syringolin A: Action on Plants, Regulationof Biosynthesis, and Phylogenetic Occurrenceof Structurally Related Compounds

摘要

Syringolin A, the product of a mixed non-ribosomal peptide/polyketidesynthetase, is secreted by Pseudomonas syringae pv. syringae under in plantaconditions and is one of the molecular determinants recognized by nonhost plantspecies. Spray application of syringolin A onto powdery mildew-infected wheatand Arabidopsis has the remarkable effect of reprogramming epidermal cellsthat are colonized by the powdery mildew fungi Blumeria graminis f. sp. triticiand Erysiphe cichoracearum, respectively,in a compatible interaction to undergohypersensitive cell death. No hypersensitive cell death is observed if the compoundis applied onto uninfected plants. Transcriptome analyses in wheat and Arabidopsiswith regard to powdery mildew inoculation and/or syringolin A spraying lead to ahypothesis about how syringolin A may accomplish to induce the hypersensitivereaction (HR) in colonized cells. The model is supported by transcriptome analysisof an Arabidopsis mutant in which HR is not induced upon syringolin A sprayingof powdery mildew-infected plants. Cloning of the syringolin A synthetase geneshas allowed us to build a detailed model of syringolin A synthesis based on thegene structure. This model in turn enabled us to clone the genes responsible forthe synthesis of glidobactins (syn. cepafungins), antibiotics with a structure relatedto syringolin A that were reported to have antitumor activity, from an unknownspecies belonging to the order Burkholderiales. Comparisons to the approximately700 complete eubacterial genomic sequences known resulted in the identificationof a small but very intriguing group of pathogenic bacteria postulated to produceglidobactin-like molecules.