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Fig. 8. WOX gene expression dynamics during early embryo patterning.
First, the egg cell and the zygote express WOX2 and WOX8. A
hypothetical polar distribution of the respective RNAs, or factors regulating
their expression, is shown. After division of the zygote, WOX2
expression is restricted to the apical daughter cell, which will give rise to
the embryo proper, whereas WOX8 expression, together with
WOX9, is restricted to the basal daughter cell, which will form the
suspensor and the hypophysis. At the 8-cell stage, the basic domains of the
embryo can be distinguished by different WOX gene expression
profiles: (1) the apical domain that will give rise to most of the shoot
expresses only WOX2, (2) the central domain that will form the
hypocotyl and part of the root expresses WOX9 (and briefly low levels
of WOX2 not illustrated here), (3) the hypophysis from which part of
the root meristem will derive expresses WOX8 and WOX9, and
(4) the suspensor expresses only WOX8. a, apical daughter cell of the
zygote; ad, apical embryo domain; b, basal daughter cell of the zygote; cd,
central embryo domain, hy, hypophyseal cell; su, suspensor.
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