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Scientists use molecular "gene trap" to identify dozens of genes involved in
the regulation of flower development, August 2005.

Identifying genes based on patterns of gene expression in specific organs
or at specific stages of development is a useful approach to improving our
understanding of complex biological processes.

Scientists Vivian Irish at Yale University in Connecticut, Rob Martienssen
at Cold Spring Harbor Laboratory in New York, and their colleagues used a
strategy known as "gene trapping" to identify numerous genes involved in the
regulation of flower development in the model plant Arabidopsis thaliana.
The research is reported in a paper by Nakayama et al. in the September
issue of The Plant Cell. The gene trap technique involves genetic
transformation of Arabidopsis plants with a reporter gene whose activity is
visualized in a simple assay, leading to the rapid identification of genes
that show specific patterns of expression. In this case, the researchers
isolated 80 different gene trap Arabidopsis lines identifying genes that
show distinct patterns of expression in flower petals and/or stamens (the
pollen-bearing organs). The research is one of the first large-scale gene
trap studies in the area of flower development, and provides extensive
information on many genes likely to have critical roles in this essential
stage of plant reproduction.

Genes provide the blueprints for proteins that carry out the functions of
living cells. In any particular organ or tissue at any particular stage of
development, gene activity may be "on" (expressing the messenger RNA
transcripts that lead to production of the corresponding protein) or "off"
(no expression). Examining gene expression patterns therefore provides
information on gene function. Gene trapping is an alternative to methods
such as DNA microarray analysis for the detection of differentially
expressed genes, and has the advantage of identifying subtle differences in
expression patterns within target organs. For example, genes expressed only
in stamen tissue during the early stages of pollen development are likely to
have an important function in controlling pollen formation.

The gene trap technique used by Drs. Irish and Martienssen involved genetic
transformation of Arabidopsis plants with the reporter gene â-glucuronidase
(GUS) lacking an external promoter sequence to drive gene expression. Each
transformation event leads to insertion of the GUS gene at a random site
within the plant genome. All endogenous genes contain promoter sequences
that determine where and when they will be expressed in an organism. The
reporter GUS gene, lacking its own promoter, will only be expressed and
produce the GUS protein if it happens to be inserted into the plant genome
in the immediate vicinity of an endogenous gene promoter. GUS activity is
assayed in transformed plants by treating harvested seedlings with a stain
that turns blue in the presence of GUS. Successful "gene trapped" plants
will show the characteristic blue stain in specific patterns in the organs
or tissues of interest. The endogenous gene corresponding to the trapped
promoter can be fished out of the genome and sequenced based on its
proximity to the inserted reporter gene. Further experiments can then be
conducted, for example, to examine the expression of the native gene in wild
type plants and to investigate gene function by creating mutant plants that
either lack expression of or overproduce the native protein.

As noted by Dr. Martienssen "gene traps are powerful tools to examine both
gene expression and gene function in animal and plant systems. Large scale
studies like this are going to provide valuable information concerning
regulatory networks and target genes". Dr. Irish added "using the gene
trapping strategy, we have identified a host of new genes involved in floral
development, as well as illuminating some of the processes involved in
establishing different tissues and organs. This general approach is very
effective in providing novel insights into development that are not easily
gleaned using other available techniques."

Many of the trapped genes were sequenced and identified, giving clues about
how they might function in petal and stamen development. Floral organ
development depends on appropriate specification and differentiation of the
unique organ identities (e.g. petals, stamens, ovules). An interesting
aspect of this research is the finding that the expression of many trapped
genes is restricted to particular subdomains of the proximodistal axis of
petals and stamens, implying that intensive regulation of patterning along
this axis is critical for floral organ development.

This research is an excellent example of how modern molecular biology
techniques help to increase our understanding of complex biological
processes.

The research paper cited in this report is available at the following link:
[www.aspb.org]

[www.aspb.org]

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