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. 2009 Nov 12;7:e0126. doi: 10.1199/tab.0126

Figure 5.

Figure 5.

Apical-basal WOX expression domains.

(A-E) Expression domains of WUSCHEL-RELATED HOMEOBOX (WOX) genes during the early stages of embryogenesis and development from the single-celled zygote. Images A–E are redrawn after Haecker et al. (2004) and Nawy et al. (2008).

(A) The zygote expressing WOX2 (green) and WOX8 (yellow), which subsequently mark the apical and basal daughter cells of the first division (B).

(B) WOX9 is upregulated in the basal cell at this time.

(C) After division of the basal cell, WOX9 is expressed only in the more apical cell, while WOX8 is expressed in both daughter cells.

(D) At the octant stage, the upper and lower tiers of embryo proper are marked by WOX2 and WOX9 expression, respectively. Both WOX8 and 9 are expressed in the hypophysis.

(E) At the dermatogen stage WOX9 expression is downregulated in the embryo proper, except for the outer cells of the lower tier. Simultaneously, WUSCHEL is turned on in the inner cells of the upper tier and WOX5 within the hypophysis.

(F–I) The fundamental fate decision that leads to the separation of apical and basal cells with differing characteristics is dependent on the YODA/MPK (YDA/MPK) pathway and may also be regulated by WOX gene expression.

(F) Apical (a) and basal (b) cell proportions in wildtype.

(G, H) Loss of YDA or SHORT SUSPENSOR (SSP) function appears to allow apical cell fate to be expressed in the basal cell and its descendants. In these mutants elongation of the zygote is suppressed and subsequent division and development of the suspensor from the basal cell is affected. Images F–H reproduced from Bayer et al. (2009) with permission from the American Association for the Advancement of Science.

(I) In wox8 wox9 double mutants, WOX2 and other apical cell lineage features are not expressed. Expression of WOX2 seems to be instrumental in apicalfate acquisition, because targeted mis-expression of WOX2 confers apical-cell features. Scale bars in I=10µm. Image reproduced from Breuninger et al. (2008) with permission from Elsevier Limited.