In higher plants, the Dof transcription factors that harbour a conserved plant-specific DNA-binding domain function in the regulation of diverse biological processes that are unique to plants. Although these factors are present in both higher and lower plants, they have not yet been characterized in lower plants. Here six genes encoding Dof transcription factors in the moss Physcomitrella patens are characterized and two of these genes, PpDof1 and PpDof2, are functionally analysed. The targeted disruption of PpDof1 caused delayed or reduced gametophore formation, accompanied by an effect on development of the caulonema from the chloronema. Furthermore, the ppdof1 disruptants were found to form smaller colonies with a reduced frequency of branching of protonemal filaments, depending on the nutrients in the media. Most of these phenotypes were not apparent in the ppdof2 disruptant, although the ppdof2 disruptants also formed smaller colonies on a particular medium. Transcriptional repressor activity of PpDof1 and PpDof2 and modified expression of a number of genes in the ppdof disruptant lines were also shown. These results thus suggest that the PpDof1 transcriptional repressor has a role in controlling nutrient-dependent filament growth.

The Dof-type transcriptional repressors CYCLING DOF FACTORS (CDFs) directly suppress the expression of CONSTANS (CO), which encodes a key regulator of photoperiodic gene expression, day-length perception and the floral transition in Arabidopsis thaliana. The genes encoding CDF-like (PpDof3 and PpDof4) and CO-like (PpCOL1-PpCOL3) proteins are present in the genome of the moss Physcomitrella patens, although P. patens lacks the genes encoding homologues of FLAVIN-BINDING KELCH REPEAT F-BOX1 (FKF1) and GIGANTEA (GI), which control the stability of CDFs in A. thaliana. In the current study, we investigated whether the functions of PpDof3 and PpDof4 are associated with the expression of PpCOL1-PpCOL3 in P. patens. We found that the diurnal expression patterns of PpDof3 and PpDof4 are similar to those of CDF genes and that like CDF1 from A. thaliana, PpDof3 and PpDof4 function as transcriptional repressors. However, targeted disruptions of PpDof3 and PpDof4 did not affect the expression of PpCOL1-PpCOL3, indicating that the expression of COLs is independent of the functions of PpDof3 and PpDof4 in P. patens.