Retinoic acid signalling is generally considered to be of animal origin. Recently, retinoic acid has been identified in cyanobacteria, yet no mechanism for its production has been identified. Here, we characterise for the first time a cyanobacterial aldehyde dehydrogenase that produces retinoic acid in vitro. Our computational studies suggest that the cyanobacterial aldehyde dehydrogenase resembles an ancestor of both eukaryotic aldehyde dehydrogenase 1 and aldehyde dehydrogenase 2. The Chlorogloeopsis fritschii aldehyde dehydrogenase described here may find applications in synthetic production of retinoic acid as well as contributing to our understanding of retinoid synthesis in cyanobacteria. (C) 2018 Elsevier Inc. All rights reserved.