Novel insights into mannitol metabolism in the fungal plant pathogen Botrytis cinerea

International audienceIn order to redefine the mannitol pathway in the necrotrophic plant pathogen Botrytis cinerea, we used a targeted deletion strategy of genes encoding two proteins of mannitol metabolism, a mannitol dehydrogenase (BcMTDH), and a mannitol-1-phosphate dehydrogenase (BcMPD). Mobilization of mannitol and quantification of Bcmpd and Bcmtdh gene transcripts during development and osmotic stress confirmed a role for mannitol as temporary and disposable carbon storage compound. In order to study metabolic fluxes, we followed conversion of labelled hexoses by wild type and Bcmpd and Bcmtdh mutant strains by in vivo NMR spectroscopy. Our data revealed that glucose and fructose were metabolized via the BcMPD and BcMTDH pathways, respectively. Existence of a novel mannitol phosphorylation pathway was suggested by NMR investigations for the first time. This last finding definitively challenged the existence of the originally postulated mannitol cycle in favor of two simultaneously expressed pathways. Finally, physiological and biochemical studies conducted on double deletion mutants (Bcmpd/Bcmtdh) showed that mannitol was still produced despite a complete alteration of both mannitol biosynthesis pathways. This strongly suggests that one or several additional undescribed pathways could participate to mannitol metabolism in B. cinerea