Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Oral Communication Abstract

DAG1 AND DAG2: DOF TRANSCRIPTION FACTORS INVOLVED IN GERMINATION

GUALBERTI G., PAPI M., RICCI I., COSTANTINO P. VITTORIOSO P.

Dipartimento di Genetica e Biologia Molecolare, Università di Roma La Sapienza, P.le A. Moro 5, 00185 Roma

The Dof proteins are transcription factors widely distributed within (and only) the plant kingdom, characterized by a strongly conserved domain encompassing a C2-X21-C2 zinc finger followed by a conserved domain. The unusual conservation of this domain, coupled with the presence of the Dof transcription factors in all plants, suggests a crucial role of these proteins in regulating different functions typical of and of universal relevance in plants.

By means of a reverse genetics approach, we demonstrated that the Arabidopsis Dof protein DAG1 is involved in the control of red light-dependent seed germination (Papi et al., Gen. & Dev., 14, 28-33 (2000) The DAG1 gene is expressed in the phloem of developing siliques but not in the embryo, showing maternal control of seed germination. The phytochrome–mediated pathway for seed germination is still required in dag1 mutant seeds as a far-red light pulse is inhibitory.

We subsequently identified a T-DNA insertion line in another uncharacterized gene of the Arabidopsis Dof family, and the corresponding gene was denominated DAG2 for its sequence similarity with DAG1 (76,2% aminoacidic identity on the whole protein). dag2 was shown to be a knock-about mutant, as the N-terminus of DAG2 is expressed in translational fusion with the GUS reporter gene. The DAG1 and DAG2 genes show also a very conserved organization, although the two genes map on different chromosomes; in fact both have a characteristic intron in the same position. Furthermore, both DAG1 and DAG2 show a tissue-specific expression localized in the vascular tissue in the whole plant. The dag2 mutant line is less sensitive to all the parameters that promote germination, such as vernalization, light and GAs, thus showing an opposite phenotype as compared to dag1.

DAG1 and DAG2 might thus be involved in interacting pathways or even regulate with opposite roles the same gene(s), based on their overlapping expression patterns and on the opposite phenotype of the respective mutants.

We have performed an ESTs-microarray screening to identify genes that are differentially expressed in the dag1 and dag2 mutant plants as compared to the wild type, with the aim of identifying the targets of DAG1 and DAG2. This will allow to shed light on the mechanism of red light–induced seed germination in Arabidopsis and to establish whether DAG2 and DAG1 have opposite effects in controlling the same regulatory circuits. In addition, ongoing transient expression experiments by particle gun transformation with different GUS- and LUC-based constructs will assess the respective regulatory roles of the DAG1 and DAG2 proteins.