Genomics of Loblolly Pine Embryogenesis
The
formation of embryos within the seeds of pine trees differs from
seed formation in traditional crop and vegetable plants.
While in both cases an embryo forms inside a seed, develops and finally germinates
to form a plant, the morphology, biochemistry and genetics of the processes
in gymnosperms (e.g. pine) and angiosperms (e.g. carrot) are distinctly different.
Embryogenesis is
the result of a regulated program of gene activity and
the elucidation of the
program for loblolly pine is the goal of this project.
The multiplication of pine embryos in a laboratory setting and the production
of plantlets, has great
implications for reforestation.
After corn, forest products are the second
most valuable US agricultural product. Loblolly pine
(Pinus taeda L.) is the
primary commercial species in southern conifer forests
covering 13.4 million
hectares, and over 1.5 billion loblolly pine seedlings
are planted annually.
Somatic embryogenesis, a tissue culture technique for
embryo multiplication, is
an excellent experimental tool for investigating embryogenesis
in this tree.
However, success of the technique is genotype-dependent
and remains
inefficient. Knowledge of the program of gene expression
in natural and
laboratory-cultivated embryos will provide insight into
varying metabolism of
these embryos and a basis for protocol improvement.
A cDNA library will
be created from loblolly pine zygotic (natural) and
somatic
(laboratory-cultivated) embryos. Together, these
will represent a combined set
of transcripts expressed during all stages of embryogenesis,
thus giving a
'snapshot' of genes participating in the formation of
the pine embryo. Randomly
selected cDNA clones will be 5' end-sequenced to generate
35,000 Expressed
Sequence Tags or ESTs. These ESTs will be clustered
and assembled to construct
a non-redundant pine EST database (TIGR Gene Index).
The non-redundant
cDNA clone set will be used to obtain gene expression
profiles during various
stages of zygotic and somatic loblolly pine embryogenesis.
This approach should
identify the genes active in embryogenesis allow determination
of their
identities and temporal expression patterns. A comparison
of profiles from
laboratory-grown and natural embryos will allow insights
into embryogenesis to
be gained, and further development of improved protocols
for loblolly pine
somatic embryogenesis. Together, these data will provide
the first detailed
overview of genome-wide gene expression patterns in
conifer embryo development.
In the long-term, this kind of information will be useful
in developing
strategies to accelerate clonal propagation.
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