Expression dynamics ofWOXgenes mark cell fate decisions during early embryonic patterning inArabidopsis thaliana

Abstract

During embryonic pattern formation, the main body axes are established and cells of different developmental fates are specified from a single-cell zygote. Despite the fundamental importance of this process, in plants, the underlying mechanisms are largely unknown. We show that expression dynamics of novel WOX (WUSCHEL related homeobox) gene family members reveal early embryonic patterning events in Arabidopsis. WOX2 and WOX8 are co-expressed in the egg cell and zygote and become confined to the apical and basal daughter cells of the zygote, respectively, by its asymmetric division. WOX2 not only marks apical descendants of the zygote, but is also functionally required for their correct development,suggesting that the asymmetric division of the plant zygote separates determinants of apical and basal cell fates. WOX9 expression is initiated in the basal daughter cell of the zygote and subsequently shifts into the descendants of the apical daughter apparently in response to signaling from the embryo proper. Expression of WOX5 shows that identity of the quiescent center is initiated very early in the hypophyseal cell, and highlights molecular and developmental similarities between the stem cell niches of root and shoot meristems. Together, our data suggest that during plant embryogenesis region-specific transcription programs are initiated very early in single precursor cells and that WOX genes play an important role in this process.

Tobacco Transcription Factors: Novel Insights into Transcriptional Regulation in the Solanaceae

“…The combined results from all searches revealed a minimum of 129 homeodomain genes in tobacco. The tobacco homeodomain gene family is similar to the plant homeodomain families in other higher plants (Chan et al, 1998;Haecker et al, 2004;Hake et al, 2004;Prigge et al, 2005) and can be divided into nine major subgroups, the knotted class 1, knotted class 2, PHD finger, Bell, glabra, HDZip class 1, HDZip class 2, HDZip class 3, and WOX classes (Supplemental Fig. S2).…”

Embryogenesis: Pattern Formation from a Single Cell

“…Early cell fate decisions that separate differing domains along the apical-basal axis are refl ected in the differential expression of members of the WUSCHEL (WUS) family of homeodomain transcription factors ( (Haecker et al, 2004); Figure 5A-E). After the initial asymmetric division of the zygote the apical cell is marked by WUSCHEL RELATED HOMEOBOX2 (WOX2) expression and the basal cell by expression of WOX8 and WOX9.…”

“…During subsequent divisions, WOX2 comes to mark the u.t., WOX9 the outer cells of the l.t. and the hypophysis, and WOX8 the hypophysis and suspensor (Haecker et al, 2004). WOX8 and WOX9 are closely related homologues that affect patterning and cell division in both the apical and basal cell lineages (Haecker et al, 2004;Wu et al, 2007;Breuninger et al, 2008).…”

“…and the hypophysis, and WOX8 the hypophysis and suspensor (Haecker et al, 2004). WOX8 and WOX9 are closely related homologues that affect patterning and cell division in both the apical and basal cell lineages (Haecker et al, 2004;Wu et al, 2007;Breuninger et al, 2008). Functions of WOX8 and WOX9 in the apical domain appear to be at least partly mediated by downstream activation of WOX2 expression, which is absent in the embryo of wox8 wox9 double mutants (Breuninger et al, 2008).…”

Regulatory Networks Involving YABBY Genes in Rice Shoot Development

“…9 The WUS-related homeobox genes (WOX) are suggested to play an important role in region-specific transcription programs early during embryogenesis and lateral organ development in Arabidopsis. 10 However, none of the isolated rice or maize WUS orthologues displays an organizing center-type expression pattern in the vegetative SAM as in Arabidopsis, 11 while the WOX orthologues from Arabidopsis (PRS) and maize (narrow sheath1/narrow sheath2, NS1/NS2) genes have been shown to function in a lateral domain of the SAM for lateral organ formation. 12,13 This suggests that both functional divergence and conservation could be attributed to this class of transcription regulators.…”