The DAG1 and DAG2 Dof zinc finger genes influence with opposite effects germination of Arabidopsis seeds

The Dof proteins are a family of plant transcription factors ubiquitously present in plants, but absent from yeast and animals. These proteins are characterised by a strikingly conserved (Dof) domain containing a single zinc finger and a downstream basic region. All Dof proteins bind similar DNA target sequences with a CTTT core. By means of a reverse genetics approach, we demonstrated that the Dof genes DAG1 and DAG2 are both involved, but with opposite roles, in the control of Arabidopsis seed dormancy and germination. In particular, inactivation of DAG1 considerably increases the germination capability of the seeds, while mutation of DAG2 results in seeds with a substantially lower germination potential than the wild type. All the physical and hormonal stimuli known to promote germination are almost superflous for dag1 seeds, whereas for dag2 seeds they are more essential than for the WT. The DAG1 and DAG2 proteins share an identical Dof domain and a high degree (77%) of aminoacid identity outside the domain. Furthermore, the DAG1 and DAG2 genes have identical expression patterns, limited to the vascular system of the mother plant but not of the embryo. This is in good agreement with the maternal effect of both the dag1 and the dag2 mutations. In addition, DAG1 is epistatic over DAG2. These evidences allow to formulate a model whereby the zinc finger proteins DAG1 and DAG2 act on a maternal switch that controls seed germination, possibly by regulating the same gene(s).