download report - Istituto Pasteur

P a r t i c i p a n t s :
Paola Vittorioso, professor; Sabrina Sabatini, researcher;
Maura Cardarelli, CNR researcher.
C o l l a b o r a t i o n s :
Dipartimento di Biologia Vegetale, Sapienza-Università di Roma
(Prof. M.M. Altamura); Institute for Chemical Research, Kyoto
University, Japan (Prof. Takashi Aoyama).
Report of activity
The Dof proteins are transcription factors present
only in plants and characterized by a strongly conserved
single zinc finger domain. We have shown
that two of these genes, DAG1 and DAG2 are
involved in regulating the germination of seeds in
Arabidopsis.
Another Dof gene, NtBBF1, is involved in auxininducible
gene expression in plant meristems.
Currently our interests are focused on a) defining the
role of DAG1 and DAG2 in regulating phytochrome
B-mediated seed germination; b) defining the role of
auxin in the development of the floral stamen; c)
defining the role of auxin and cytokinin, and of
genes responsive to these hormones in the maintenance
of the root meristem.
DAG1
Previous data showed that inactivation of the gene
encoding the Arabidopsis thaliana transcription factor
DOF AFFECTING GERMINATION 1 (DAG1),
renders seed germination more sensitive to both
Phytochrome B (PhyB) and gibberellins (GA). dag1
mutant seeds require less red (R) light fluence and a
lower GA concentration than wild type to germinate.
In the last year we found that inactivation of the
gene PHYTOCHROME INTERACTING FACTOR
3-LIKE 5 (PIL5) results in down-regulation of
DAG1. Moreover, inactivation of PIL5 in the dag1
mutant background further increased the germina-
39
Molecular genetics of eukaryotes - AREA 3
The role of the DAG transcription factors in Arabidopsis seed
germination
Principal investigator: Paolo Costantino
Professor of Molecular Biology
Dipartimento di Genetica e Biologia Molecolare
Tel: (+39) 06 4455344, 06 49912411; Fax: (+39) 06 4440812
paolo.costantino@uniroma1.it
tion potential of dag1 mutant seeds, confirming that
DAG1 is under the positive control of PIL5. On the
other hand, germination of dag1 phyB double mutant
seeds showed a reduced requirement of gibberellins
(GA) as compared to phyB mutant seeds, both in the
presence and in the absence of endogenous GA
biosynthesis. Furthermore, the GA biosynthetic
gene AtGA3ox1 is upregulated in dag1 seeds as compared
to the wild type, and DAG1 inactivation also
affects the expression of different ABA metabolic
genes. These data suggest that DAG1 is a negative
regulatory element acting downstream of PIL5 in
the PhyB signal transduction pathway that regulates
GA and ABA metabolic genes during seed germination.
In addition, based on the analysis of hypocotyls
of dag1 and phyB mutant plantlets, of plantlets overexpressing
PhyB in the dag1 mutant as well as of
dag1 phyB double mutants, we suggest that DAG1
may act as a negative regulatory element downstream
of PhyB also in hypocotyl elongation.
Hormones & stamen development
Different hormones are involved in different stages
of the development of the different floral organs. We
analyzed the localization, synthesis, transport, and
effects of auxin on the processes occurring late in the
development of the Arabidopsis stamen: anther
dehiscence, pollen maturation, and preanthesis filament
elongation. Expression of auxin-sensitive
reporter constructs suggests that auxin effects begin
in anthers between the end of meiosis and the bilocular
stage in the somatic tissues involved in the first
step of dehiscence as well as in the microspores and
in the junction region between anther and filament.
In situ hybridizations of the auxin biosynthetic
genes YUC2 and YUC6 suggest that auxin is synthesized
in anthers. In agreement with the timing of
auxin effects, the TIR1, AFB1, AFB2, and AFB3
auxin receptor-encoding genes are transcribed in
anthers only during late stages of development
starting at the end of meiosis. We found that in tir1