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Flavonoids are widely distributed in nature and many studies have revealed that some flavonoids have antibiotic activity against fungal plant infection. Fungi can however also produce enzymes that metabolize and detoxify these plant chemical defenses. The phytopathogenic fungus Sclerotinia sclerotiorum is a devastating necrotrophic pathogen that can cause stem rot disease in a vast range of plant species and results in large losses of crop yields worldwide. In order to determine how A.thaliana interacts with S.sclerotiorum, changes in the levels of defense compounds (glucosinolates, flavonoids, camalexin and coumaroyl agmatine) in A. thaliana was investigated. HPLC analyses showed that the concentration of total flavonoids in A. thaliana inoculated with the aggressive strains UF-70 decreased 3 days post inoculation when compared with mock inoculated A. thaliana. The result suggested that S. sclerotiorum may have strategy to block accumulation of flavonoids in host plant.
An in vitro growth experiment with artificial medium which contained different phenolic compounds showed that S. sclerotiorum can degrade quercetin and kaempferol (which are precursors of flavonoids biosynthesis) more quickly than others. Therefore the candidate gene encoding an enzyme involved in degradation of quercetin and kaempferol of S. sclerotiorum was identified and named SsQDO. In order to investigate the role of this flavonoid degradation gene in fungal virluence, a SsQDO knock-out mutant ΔQDO was generated based on wild type UF-70. The ability to degrade quercetin and kaempferol in the mutant was deleted but the growth rate of mycelium was not affected. Inoculation with A. thaliana showed that QDO knock-out mutants decreased pathogenicity.
Our results suggested that polyphenol degradation may play an important role in virulence and survival of S. sclerotiorum during interation with host plant.
last updated on 2018-01-30