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identification of genes expressed in the embryo sac remains cumbersome be-
cause of its inherent microscopic and inaccessible nature. We used genetic sub-
traction and comparative profiling by microarray between the Arabidopsis
thaliana wild-type and a sporophytic mutant lacking an embryo sac in or-
der to identify embryo sac expressed genes in this model organism. The influ-
ences of the embryo sac on the surrounding sporophytic tissues were previously
thought to be negligible or nonexistent; we investigated the extent of these in-
teractions by transcriptome analysis.
Results
We identified 1,260 genes as embryo sac expressed by analyzing both our
dataset and a recently reported dataset, obtained by a similar approach, us-
ing three statistical procedures. Spatial expression of nine genes (for instance
a central cell expressed trithorax-like gene, an egg cell expressed gene encoding
a kinase, and a synergid expressed gene encoding a permease) validated our
approach. We analyzed mutants in five of the newly identified genes that ex-
hibited developmental anomalies during reproductive development. A total of
527 genes were identified for their expression in ovules of mutants lacking an
embryo sac, at levels that were twofold higher than in the wild type.
Conclusion
Identification of embryo sac expressed genes establishes a basis for the func-
tional dissection of embryo sac development and function. Sporophytic gain of
expression in mutants lacking an embryo sac suggests that a substantial por-
tion of the sporophytic transcriptome involved in carpel and ovule develop-
ment is, unexpectedly, under the indirect influence of the embryo sac.
Background
The life cycle of plants alternates between diploid (sporophyte) and haploid (male
and female gametophytes) generations. The multicellular gametophytes repre-
sent the haploid phase of the life cycle between meiosis and fertilization, during
which the gametes are produced through mitotic divisions. Double fertilization
is unique to flowering plants; the female gametes, namely the haploid egg cell
and the homo-diploid central cell, are fertilized by one sperm cell each. Double
fertilization produces a diploid embryo and a triploid endosperm, which are the
two major constituents of the developing seed [1]. The egg, the central cell, and
two accessory cell types (specifically, two synergid cells and three antipodal cells)
are contained in the embryo sac, also known as the female gametophyte or mega-
gametophyte, which is embedded within the maternal tissues of the ovule. As a
carrier of maternal cell types required for fertilization, the embryo sac provides an
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