Mutations in the Dof zinc finger genes DAG2 and DAG1 influence with opposite effects the germination of Arabidopsis seeds

We describe the Arabidopsis gene DAG2 encoding a Dof zinc finger protein and show that it is involved in the control of seed germination. An Arabidopsis mutant line with a T-DNA insertion in DAG2 isolated by reverse genetics produces seeds that are substantially more dependent than the wild type on the physical stimuli-light and cold treatment-that promote germination. Mutant dag2 seeds also are less sensitive to the germination-promotive effect of gibberellins, because a 10-fold higher amount of gibberellins is needed to restore germination when endogenous gibberellin biosynthesis is blocked. The seed germination characteristics of the dag2 mutant are opposite to those of dag1, a knockout mutant of another Dof gene (DAG1) that we showed previously to be involved in the control of seed germination, and are similar to those of plants that overexpress DAG1. The promoter of the DAG2 gene is active specifically in the vascular system of the mother plant but not in the embryo, and segregation analysis indicates that the effect of the dag2 mutation is maternal. Both characteristics are in common with DAG1; additionally, the DAG1 and DAG2 proteins share high sequence homology and an identical zinc finger domain. These data suggest, and the germination phenotype of the double mutant is compatible with, 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).