S. Yanagisawa, Dof1 and Dof2 transcription factors are associated with expression of multiple genes involved in carbon metabolism in maize, PLANT J, 21(3), 2000, pp. 281-288
Dof proteins are transcription factors that appear to be unique to plants.
Maize Dof1 has been suggested to be a regulator for C4 photosynthetic phosp
hoenolpyruvate carboxylase (C4PEPC) gene expression. The present study demo
nstrates that Dof1 also enhances transcription from the promoters of both c
ytosolic orthophosphate dikinase (cyPPDK) genes and a non-photosynthetic PE
PC gene, which are not present in animals. Expression of Dof1-specific anti
sense RNA or the DNA-binding domain of Dof1 alone reduced the activities of
these promoters in maize leaf protoplasts. Electrophoretic mobility shift
assays revealed several Dof1-binding sites in these promoters. The cyppdk1
promoter contained two Dof1-binding sites, one of which was linked to the b
inding site of a plant bZIP protein. By using deleted or mutated cyppdk1 pr
omoters, both Dof1-binding sites were shown to be functional. Furthermore,
Dof1 elevated the activities of the cyppdk and pepc promoters more strongly
in greening protoplasts than in etiolated protoplasts, in accordance with
the different activities of these promoters in two types of protoplasts. An
other Dof protein of maize, Dof2, suppressed the activity of the C4pepc pro
moter but was able to activate certain other promoters. These results sugge
st that Dof proteins may play regulatory roles in multiple gene expressions
associated with the plant-specific pathway for carbon metabolism in maize.
In addition, the primary characteristic of Dof proteins, i.e. different ac
tivities in distinct types of cells and opposite actions on promoters in di
fferent contexts, suggests the potential of Dof proteins to differentially
regulate diverse promoters in a variety of plant tissues. Speculation raise
d by these results concerning the evolution of the C4pepc gene is also disc
ussed.