Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: 49pg1
PROGRESS TOWARDS THE POSITIONAL CLONING OF THE ARABIDOPSIS
DE-ETIOLATED -1 (DET1) GENE.
Terrence Delaney, Alan Pepper, Dan Pole, Tracy Washburn and
Joanne Chory. Plant Biology Laboratory, The Salk Institute for
Biological Studies, San Diego, CA 92186-5800.
Light plays a critical role in the development of
dicotyledenous seedlings such as Arabidopsis thaliana. The light
signal is a requirement for the photomorphogenic process, which
includes the development of leaves and the maturation of
chloroplasts. During development, light signals are integrated
with intrinsic signals defining temporal and spatial specificity
of gene expression and cell differentiation. Aside from what is
known about the regulatory photoreceptors, such as phytochrome,
little is known about the signal transduction and morphogenetic
pathways that mediate light-regulated development. In an effort
to study these pathways, our laboratory has utilized a combined
molecular and genetic approach. In Arabidopsis, we have
identified a class of mutants that displays many characteristics
of a light grown plant, when grown in the dark. These mutants,
designated det (for de-etiolated), are recessive and fall into
four complementation groups. Epistasis analysis suggests that
the DET1 gene acts downstream from phytochrome and other
photoreceptors. In addition, the detl mutant is defective in
the tissue and cell specificity of photoregulated gene
expression and chloroplast differentiation. We hypothesize that
the DET1 gene product is a negatively-acting regulatory element
in the light signal transduction pathway. Additionally, the DET1
gene product may act to integrate intrinsic temporal and spatial
signals that regulate photomorphogenic development. In order to
study the mechanism of action of the DET1 gene product, we are in
the process of cloning the DET1 gene by chromosome walking
followed by complementation of the mutant phenotype with cloned
wild-type DNA sequences. The DET1 locus has been mapped to
chromosome 4, and is flanked by the RFLP markers cos2616 and
lambda 518. A chromosome walk, utilizing yeast artificial
chromosomes (YACs), has been undertaken using these RFLP probes
as starting points. Overlapping YAC clones, corresponding to
>1.7 Mbp of chromosome 4 have been isolated and characterized.
The majority of YAC end-probes from this region of the genome
display RFLPs between Columbia and Landsberg ecotypes. RFLP
analysis of Landsberg-Columbia recombinants with crossovers near
DET1 has allowed us to localize the DET1 gene to a 100-200 Kbp
segment of the walk. The isolation of T-DNA transformable
cosmid clones with Arabidopsis inserts corresponding to this
segment of the genome is currently underway.
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