Biology Reference
In-Depth Information
In about 54% of the ovules, the polar nuclei failed to fuse in kerridwin
(ken-1), a mutant allele of AT2G47750, which encodes an auxin-responsive
GH3 family protein (Figure 4 and Table 2). The corresponding wild-type
pistils exhibited 9% unfused polar nuclei when examined 2 days after emas-
culation, and the remaining ovules had one fused central cell nucleus (n =
275). The hog1-6 mutant is allelic to the recently reported hog1-4, disrupt-
ing the HOMOLOGY DEPENDENT GENE SILENCING 1 gene (HOG1;
AT4G13940), and they both were zygotic lethal, producing 24% to 26%
aborted seeds (Table 2) [55]. Both these mutants exhibit anomalies during
early endosperm division and zygote development (Figure 4i-l). In wild-type
seeds, the endosperm remains in a free-nuclear state before cellularization
around 48 to 60 hours after fertilization (HAP), and the embryo is at the
globular stage (Figure 4f ). In hog1-6, at about the same time the endosperm
nuclei displayed irregularities in size, shape and number, and they never were
uniformly spread throughout the seed (Figure 4i-l; n = 318). The irregular
mitotic nuclei were clustered into two to four domains. The zygote remained
at the single-cell stage, and in 2% of the cases it went on to the two-cell stage.
In very rare instances (five observations), two large endosperm nuclei were
observed while the embryo remained arrested at single-cell stage in hog1-4
(Figure 4k).
In omisha (oma-1) and freya (fey-1), the T-DNA disrupted AT1G80410
(encoding an acetyl-transferase) and AT5G13010 (encoding an RNA heli-
case), leading to 18% and 21% seed abortion, respectively (Table 2). The em-
bryo arrested around the globular stage in both mutants (Figure 5f-i). The ar-
rested mid-globular embryo cells (17%; n = 269) were larger in size in oma-1,
whereas the corresponding wild type progressed to late-heart and torpedo
stages with cellularized endosperm (Figure 5g). In the aborted fey-1 seeds, the
cells of late-globular embryos (19%; n = 243) were much larger and irregular
in shape than in the wild type, but no endosperm phenotype was discernible
(Figure 5i). In most cases, giant suspensor cells were seen in fey-1, and there
were more cells in the mutant suspensor than in that of the wild type (Figure
5i). ILITHYIA disrupts AT1G64790 encoding a translational activator, and
the ila-1 embryos arrested when they reached the torpedo stage (Figure 4j and
Table 2; n = 352). A small proportion of ila-1 embryos arrested at a late heart
stage (11 observations). The results from the first phase of our targeted reverse
genetic approach showed that there are mutant phenotypes for embryo sac
expressed candidate genes, and that these gene disruptions lead to lethality
during female gametophyte or seed development.
