Paper accepted: “Chitosan and chitin deacetylase activity are necessary for development and virulence of Ustilago maydis”

Today, our joint paper with the group of Prof. Regine Kahmann from the Max Planck Institute for Terrestrial Microbiology in Marburg was accepted for publication in the open access journal mBio of the American Society for Microbiology. Dr. Yanina Rizzi from the Marburg team had generated single and multiple knock-out mutants of the seven putative chitin deacetylase genes which they had identified in the genome of the fungal maize pathogen Ustilago maydis and which had been verified as such by Dr. Ratna Singh and Martin Bonin from our group. Together with our doctoral candidate Mounashree, she had produced six recombinant enzymes (one of the genes turned out to be a pseudogene) so that Mouna, supported by Dr. Stefan Cord-Landwehr, could verify the CDA activity of the recombinant proteins. Meanwhile, the group in Marburg characterised the mutants morphologically and performed extensive pathogenicity trials. Surprisingly, the knock-out of all seven genes turned out to be lethal for the fungus. This is the first time that a vital role for a CDA has been found. But surprisingly also, the knock-outs had less influence on pathogenicity than expected. Even mutants that unlike the wildtype fungus had chitin instead of chitosan in their infection hyphae were still virulent. Clearly, the stealth mechanism of converting chitin into chitosan to escape the immune system of the host plant is not the only trick the fungus plays for efficient host colonisation.