The Hypocrea jecorina (syn. Trichoderma reesei) lxr1 gene encodes a d-mannitol dehydrogenase and is not involved in l-arabinose catabolism

The Hypocrea jecorina LXR1 was described as the first fungal l-xylulose reductase responsible for NADPH dependent reduction of l-xylulose to xylitol in l-arabinose catabolism. Phylogenetic analysis now reveals that LXR1 forms a clade with fungal d-mannitol 2-dehydrogenases. Lxr1 and the orthologous Aspergillus niger mtdA are not induced by l-arabinose but expressed at low levels during growth on different carbon sources. Deletion of lxr1 does not affect growth on l-arabinose and l-xylulose reductase activity remains unaltered whereas d-mannitol 2-dehydrogenase activities are reduced. We conclude that LXR1 is a d-mannitol 2-dehydrogenase and that a true LXR1 is still awaiting discovery.