Plant Molecular Biology 37: 171–178, 1998.
1998 Kluwer Academic Publishers. Printed in Belgium.
The light-regulated Arabidopsis bZIP transcription factor gene ATB2
encodes a protein with an unusually long leucine zipper domain
, Peter Weisbeek and Sjef Smeekens
Department of Molecular Cell Biology, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands
author for correspondence);
Current address: Department of Molecular Genetics, John Innes Centre, Colney,
Norwich NR4 7UH, UK
Received 24 July 1997; accepted in revised form 2 December 1997
Key words: Arabidopsis, bZIP transcription factor, light-regulated gene expression
A light-regulated basic domain/leucine zipper gene, ATB2, was identiﬁed in an Arabidopsis thaliana transcription
factor gene collection. Both genomic and cDNA clones of ATB2 were isolated. The gene encodes a small protein
(18 kDa) which mainly consists of the basic domain and an unusually long leucine zipper. The expression of the
ATB2 gene is induced when etiolated or dark-adaptedseedlingsare transferred to the light. Moreover,its expression
is derepressedindark-grownseedlingsofthe photomorphogenicmutants cop1 and det1. In matureplants, transcript
levels are particularly high in ﬂowers and also light-responsive in these tissues.
Changes in gene expression in response to physiolo-
gical, developmental, and environmental signals in
part are mediated by the action of transcription factors.
Transcription factors are regulatory proteins that bind
ive genes, and interact with the general transcription
machinery. In response to a stimulus, speciﬁc tran-
scription factors are activated and interact with regu-
latory elements in the promoter regions of responsive
genes, which results in a speciﬁc expression pattern
of these target genes. Several classes of transcription
ily conserved structural motifs for DNA binding .
For plants, light is an important environmentalsig-
nal in the regulation of numerous developmental and
metabolic processes throughout all stages of the plants
life cycle. The effect of light on plant development
and physiology is best illustrated in seedlings. When
dark-grown seedlings are exposed to light, complex
changes in development and physiology are initiated.
These include changes in morphology like the inhib-
Thenucleotidesequencedata reportedwill appearin theEMBL,
GenBank and DDBJ Nucleotide Sequence Databases under the
accession number X99747.
ition of hypocotyl elongation, the expansion of coty-
ledons, and the differentiation of plastids into func-
tional chloroplasts. Also light-induciblegenes, like the
changes result in the establishment of the seedling as a
photoautotrophicorganism [17, 23].
In plants light is perceived by different classes of
characterized [11, 17]. They are present in two photo-
convertible forms: the red light absorbing form named
Pr, and the far-red light absorbing Pfr form. The latter
is thought to be the biologically active form, initiat-
ing the signal transduction pathway . The light-
signal transduction pathway is only partially under-
stood. Roles have been implied for heterotrimeric G-
proteins, calcium and calmodulin, and cyclic GMP
in phytochromesignalling [2, 28]. Eventually the light
signalleads to changes in gene expressionand changes
in the developmental program. We are interested in
transcription factors that play a role in this light regu-
lation of gene expression.
One speciﬁc class of transcription factors is made
up of the basic domain/leucine zipper (bZIP) proteins.
Characteristic of these proteins is a highly conserved