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order to explore the transcriptome more extensively. Here, we report the identity
of 1,260 potentially embryo sac expressed genes, 8.6% of which were not found
in tissue-specific sporophytic transcriptomes, suggesting selective expression in
the embryo sac. Strong support for the predicted transcriptome was provided by
the spatial expression pattern of 24 genes in embryo sac cells; 13 of them were
previously identified as being expressed in the embryo sac by enhancer detectors
or promoter-reporter gene fusions, and we could confirm the spatial expression
of the corresponding transcripts by microarray analysis. In addition, we show
embryo sac cell-specific expression for nine novel genes by in situ hybridization
or reporter gene fusions. In order to elucidate the functional role of the identi-
fied genes, we sought to search for mutants affecting embryo sac and seed de-
velopment by T-DNA mutagenesis. We describe the developmental anomalies
evident in five mutants exhibiting lethality during female gametogenesis or seed
development.
Genetic evidence suggests that the maternal sporophyte influences develop-
ment of the embryo sac [1,35-37]. Because the carpel and sporophytic parts of the
ovule develop normally in the absence of an embryo sac, it has been concluded
that the female gametophyte does not influence gene expression in the surround-
ing tissue [2]. Our data clearly showed that 527 genes were over-expressed by at
least twofold in the morphologically normal maternal sporophyte in two sporo-
phytic mutants lacking an embryo sac. We confirm the gain of expression of 11
such genes in mutant ovules by reverse transcription polymerase chain reaction
(RT-PCR). Spatial expression of five of these genes in carpel and ovule tissues of
coa was confirmed by in situ hybridization, revealing that expression mainly in
the carpel and ovule tissues is tightly correlated with the presence or absence of
an embryo sac. In summary, our study provides two valuable datasets of the tran-
scriptome of Arabidopsis gynoecia, comprising a total of 1,787 genes: genes that
are expressed or enriched in the embryo sac and are likely function to control em-
bryo sac and seed development; and a set of genes that are over-expressed in the
maternal sporophyte in the absence of a functional embryo sac, revealing interac-
tions between gametophytic and sporophytic tissues in the ovule and carpel.
Results
We intended to isolate genes that are expressed in the mature female gametophyte
of A. thaliana, and are thus potentially involved in its development and function.
To this end, the transcriptomes of the gynoecia from wild-type plants were com-
pared with those of two sporophytic recessive mutants, namely coatlique (coa)
and sporocyteless (spl), both of which lack a functional embryo sac. The coa mu-
tant was isolated during transposon mutagenesis for its complete female sterility
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