Ring Closure Reactions of Phenylphenalenones and Musellarins

For the second time since banana is commercially grown on large scale, banana is severely threatened by extinction by a fungal pathogen called Fusarium odoratissimum. Phenylphenalenones (PP) provide a promising dual protective strategy by acting as lead compounds for the synthesis of efficient plant protectants on the one hand and by mediating native defence mechanisms to banana species. The project will elucidate unknown steps in the biosynthesis of PPs to lay the foundation for the breeding of naturally resistant banana varieties. Therefore, a multidisciplinary approach is chosen using chemical and biological processes: The project investigates important parts of the interaction of bananas with the fungus Fusarium odoratissimum Tropical Race 4 (TR4). The cultivation of two different banana varieties with different degrees of resistance and the TR4 inoculation of the two banana varieties allows the determination of the phytochemical profiles and of the distribution of Cu and S at a cellular level. The location where these processes take place will be determined by a combination of nuclear magnetic resonance (NMR) spectroscopy, as well as different mass spectrometry- (MS) and microscopy- techniques. High-resolution transcriptome mapping of the Musa-TR4-interaction using fluorescent reporter Fusarium TR4 will be performed to generate spatially resolved gene expression maps. Single molecule fluorescent in-situ hybridization (smFISH) will be carried out to confirm spatiotemporal gene expression of selected PP/ML biosynthesis genes (polyphenol oxidases (PPOs)) in cross sections. The fundamental basic of our project are hypothetical detailed mechanistic considerations of the reaction sequences of the biosynthesis of phenylphenalenones (PPs) and musellarins (MLs), and an evaluation of the significant genetic information of the Musa genome and Musa transcriptomes. especially enabling the assignment of our key research enzymes, the PPOs. The formation of o-dihydroxy compounds and o- quinones, the subsequent ring closure reactions and the enzymatically catalyzed formation of aromatic systems will be investigated. PPOs are our key research enzyme candidates for these reaction steps. PPOs are to be processed by molecular biology and characterized by biochemical and X-ray crystal structure analysis. Finally, possible antifungal effects of PPs and MLs and their Cu complexes are to be investigated in bioassays.