Pattern Formation in the Arabidopsis Embryo Revealed by Position-Specific Lipid Transfer Protein Gene Expression.

Abstract

During Arabidopsis embryogenesis, the zygote divides asymmetrically in the future apical-basal axis; however, a radial axis is initiated only within the eight-celled embryo. Mutations in the GNOM, KNOLLE, and KEULE genes affect these processes: gnom zygotes tend to divide symmetrically; knolle embryos lack oriented cell divisions that initiate protoderm formation; and in keule embryos, an outer cell layer is present that consists of abnormally enlarged cells from early development. Pattern formation along the two axes is reflected by the position-specific expression of the Arabidopsis lipid transfer protein (AtLTPT) gene. In wild-type embryos, the AtLTPl gene is expressed in the protoderm and initially in all protodermal cells; later, AtLTPí expression is confined to the cotyledons and the upper end of the hypocotyl. Analysis of AtLTPT expression in gnom, knolle, and keule embryos showed that gnom embryos also can have no or reversed apical-basal polarity, whereas radial polarity is unaffected. knolle embryos initially lack but eventually form a radial pattern, and keule embryos are affected in protoderm cell morphology rather than in the establishment of the radial pattern. INTRODUCTIONIn flowering plants, the primary body plan of the seedling is laid down during embryogenesis (Steeves and Sussex, 1989). This body plan has been described as the superimposition of an apical-basal and a radial pattern . The apical-basal pattern visible in the seedling consists of distinct elements: two cotyledons, shoot meristem, hypocotyl, and root, including the root meristem. In Arabidopsis, the apical-basal polarity is already evident in the zygote, which elongates approximately threefold in the apical direction. An asymmetric division then generates a small apical cell from which all pattern elements are derived, except for part of the root, that is, the columella root cap and the quiescent center (Scheres et al., 1994), and the suspensor, which are derived from the larger basal cell. Mutations resulting in a deletion of regions of the apical-basal pattern include gurke, fackel, monopteros, and gnom (Mayer et al., , 1993 Berleth and Jürgens, 1993) and rootless, shoot meristemless, and topless (Barton and Poethig, 1993).In gnom embryos (Mayer et al., , 1993Busch et al., 1996), also called emb30 embryos (Shevell et al., 1994;Franzmann et al., 1995), the zygote tends to divide symmetrically, producing an enlarged apical cell at the expense of the basal cell. gnom embryos have no root meristem and reduced orno cotyledons, and most gnom seedlings are cone shaped, 'To whom correspondence should be addressed.retaining apical-basal polarity, although the pattern is severely compromised. Some gnom seedlings, however, are ball shaped, displaying no morphologically apparent apical-basal polarity (Mayer et al., 1993). The radial pattern is arranged in three concentric layers of tissues: the outer protoderm, the inner mass of ground tissue, and the centrally located vascular bundles. This pattern is initiated within the first eight cel...

Paternally inherited transgenes are down‐regulated but retain low activity during early embryogenesis in Arabidopsis

“…Following reciprocal LTP::LhG4×pOp::GUS crosses, GUS activity was absent at the globular stage and a weak activity was first noticed at the heart stage, becoming stronger at a later stage with its specific localisation at the apical pole (Fig. 2B) as previously described [6]. By contrast, embryos from self‐fertilisation of LTP::LhG4; pOp::GUS double transgenic lines display reporter gene expression as early as the octant stage (Fig.…”

“…We aimed at analysing the timing of activation of two promoters during early embryogenesis that drive distinct expression patterns: the CYC promoter (from the cyclin B AtCYCB1;1 gene [4]), and the LTP promoter (from the lipid transfer protein AtLTP1 gene [5,6]). We used CYC::GUS and LTP::GUS lines containing a transcriptional fusion of the CYC and LTP promoters with the uidA reporter gene, encoding the GUS protein.…”

Somatic Embryogenesis: Fundamental Aspects and Applications

“…26.5c). In wild-type embryos this gene was expressed in the protoderm and initially in all protodermal cells, whereas in more mature embryos AtLTP1 expression was confined to the cotyledons and the upper end of the hypocotyl (Vroemen et al 1996). 26.5c, d).…”

The syntaxin 31-induced gene, LESION SIMULATING DISEASE1 (LSD1), functions inGlycine maxdefense to the root parasiteHeterodera glycines

“…14,17,18 The roles that these core membrane fusion proteins perform in eukaryotes is extensive, ranging from signaling, cell growth, mitosis, the endocytic cycle, exocytosis, hormonal release, neurotransmission, fertilization, embryogenesis, development, sporulation and cell death. 2,3,[13][14][15][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] A variety of studies show membrane fusion to be important to the defense process that plants have toward pathogens as well as different types of defense responses. 9,11,[34][35][36][37][38][39][40][41][42] While the list of functions that the membrane fusion and vesicle transport proteins have is large, it is less clear whether the proteins also are engaged in other, but related functions.…”