Dirigent (DIR) proteins were found to mediate regio- and stereoselectivity of bimolecular phenoxy radical coupling
during lignan biosynthesis. Here we summarize the current knowledge of the importance of DIR proteins in lignan and
lignin biosynthesis and highlight their possible importance in plant development. We focus on the still rather enigmatic
Arabidopsis DIR gene family, discussing the few members with known functional importance. We comment on recent
discoveries describing the detailed structure of two DIR proteins with implications in the mechanism of DIR-mediated
catalysis. Further, we summarize the ample evidence for stress-induced dirigent gene expression, suggesting the role
of DIRs in adaptive responses. In the second part of our work, we present a preliminary bioinformatics-based charac-
terization of the AtDIR family. The phylogenetic analysis of AtDIRs complemented by comparison with DIR proteins of
mostly known function from other species allowed us to suggest possible roles for several members of this family and
identify interesting AtDIR targets for further study. Finally, based on the available metadata and our in silico analysis of
AtDIR promoters, we hypothesize about the existence of specific transcriptional controls for individual AtDIR genes
and implicate them in various stress responses, hormonal regulations, and developmental processes.
