Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 14 (23), 2938-43

A Novel Two-Component Hybrid Molecule Regulates Vascular Morphogenesis of the Arabidopsis Root

Affiliations

A Novel Two-Component Hybrid Molecule Regulates Vascular Morphogenesis of the Arabidopsis Root

A P Mähönen et al. Genes Dev.

Abstract

The developmental ontogeny of the vascular system (consisting of xylem, phloem and [pro]cambium) is poorly understood despite its central role in plant physiology. We show that in the Arabidopsis root meristem, xylem cell lineages are specified early, whereas phloem and procambium are established through a set of asymmetric cell divisions. These divisions require the WOODEN LEG (WOL) gene. The WOL gene encodes a novel two-component signal transducer with an unusual tandem arrangement of two receiver domains. It is expressed specifically in the vasculature from the early stages of embryogenesis on, consistent with a role as a sensor for vascular morphogenesis.

Figures

Figure 1
Figure 1
Cell lineages in the vascular bundle of primary root in Arabidopsis. (A–I) A cross-section series of the wild-type primary root (3-μm-thick sections). (A) At the level of the quiescent center (QC). (B) 3 μm, (C) 6 μm, (D) 9 μm, (E) 12 μm, (F) 15 μm, (G) 27 μm, (H) 69 μm, and (I) ∼120 μm above the QC. (J,K) Longitudinal sections of the wild-type and wol primary root, respectively. Cells of the QC are labeled with asterisks. Newly formed cell walls after the cell divisions in the procambium in C–G are indicated with small black arrows. The specific set of newly formed cell walls associated with phloem development (G) is indicated in red. Prospective protoxylem cells are indicated with thick arrows. (p) Pericycle; (pp) sieve elements of the protophloem. Scale bar, 30 μm. Schematic: cell lineages of the vascular bundle. The colors refer to the cell lineages only; the differentiation status of the cells is not known. The first and second maturing sieve elements are indicated as protophloem and metaphloem, respectively.
Figure 2
Figure 2
WOL is not necessary for metaxylem development. (A) wt: Metaxylem is gradually differentiating in an axis flanked by two files of protoxylem cells. (B) wol: The entire vascular bundle is differentiated as protoxylem. (C) wol × fass: Protoxylem and metaxylem organization analogous to that in wt. The confocal images were taken from whole mounts of seedlings stained with fuchsin. Scale bar, 30 μm.
Figure 3
Figure 3
Molecular cloning of the WOL locus. (A) Fine mapping. RNS1 and rga are preexisting CAPS markers in top of chromosome 2. T23K3/3 and Kin2/4 are the closest markers (designed in this study) for the wol mutation in the BAC T23K3. The number of recombination events between markers and the wol locus is indicated below the markers. Hatched bar represents the 13.8-kb MscI fragment of the T23K3 BAC clone fragment (cloned in pCOM32), which complemented the wol mutation. (B) Structure of the WOL gene. Exons are indicated as solid bars. Three combinations of dotted lines show the alternative splicing variations of the WOL gene (deposited in GenBank). All result in the identical longest open reading frame with an ATG in position 13572–13574 of the BAC T23K3. The wol mutation is located in the third exon (asterisk), where it is converting T278 (ACT) to I278 (ATT). The small hatched bar represents the 256-bp probe used in hybridization analyses. (C) Complementation of the wol mutation. Left to right: Cross sections of wol, wol transformed with the pCOM32 construct, and wild-type primary roots. (Arrows) Protoxylem in wild-type and rescued root; (p) pericycle; (pp) sieve elements of protophloem. Scale bar, 30 μm. (D) Predicted domain structure of WOL. Extracellular receptor domain (hatched bar) is located near the N terminus between the two transmembrane regions (vertical solid bars). C-terminal domain consists of a histidine kinase domain (H) and two receiver domains (DA and DB). (E) Amino acid sequence alignment representing a region surrounding the wol mutation site in the putative receptor domain of three WOL-like proteins (WOL, F17L21.11, MXH1.16) and Dictyostelium discoideum DHKA. Identical amino acids are indicated by black boxes. The altered amino acid residue in wol (I278) is shown above the alignment. (F) Northern blot of total RNA from wild-type roots and shoots. Ethidium bromide–stained ribosomal RNA is shown as a loading control.
Figure 3
Figure 3
Molecular cloning of the WOL locus. (A) Fine mapping. RNS1 and rga are preexisting CAPS markers in top of chromosome 2. T23K3/3 and Kin2/4 are the closest markers (designed in this study) for the wol mutation in the BAC T23K3. The number of recombination events between markers and the wol locus is indicated below the markers. Hatched bar represents the 13.8-kb MscI fragment of the T23K3 BAC clone fragment (cloned in pCOM32), which complemented the wol mutation. (B) Structure of the WOL gene. Exons are indicated as solid bars. Three combinations of dotted lines show the alternative splicing variations of the WOL gene (deposited in GenBank). All result in the identical longest open reading frame with an ATG in position 13572–13574 of the BAC T23K3. The wol mutation is located in the third exon (asterisk), where it is converting T278 (ACT) to I278 (ATT). The small hatched bar represents the 256-bp probe used in hybridization analyses. (C) Complementation of the wol mutation. Left to right: Cross sections of wol, wol transformed with the pCOM32 construct, and wild-type primary roots. (Arrows) Protoxylem in wild-type and rescued root; (p) pericycle; (pp) sieve elements of protophloem. Scale bar, 30 μm. (D) Predicted domain structure of WOL. Extracellular receptor domain (hatched bar) is located near the N terminus between the two transmembrane regions (vertical solid bars). C-terminal domain consists of a histidine kinase domain (H) and two receiver domains (DA and DB). (E) Amino acid sequence alignment representing a region surrounding the wol mutation site in the putative receptor domain of three WOL-like proteins (WOL, F17L21.11, MXH1.16) and Dictyostelium discoideum DHKA. Identical amino acids are indicated by black boxes. The altered amino acid residue in wol (I278) is shown above the alignment. (F) Northern blot of total RNA from wild-type roots and shoots. Ethidium bromide–stained ribosomal RNA is shown as a loading control.
Figure 3
Figure 3
Molecular cloning of the WOL locus. (A) Fine mapping. RNS1 and rga are preexisting CAPS markers in top of chromosome 2. T23K3/3 and Kin2/4 are the closest markers (designed in this study) for the wol mutation in the BAC T23K3. The number of recombination events between markers and the wol locus is indicated below the markers. Hatched bar represents the 13.8-kb MscI fragment of the T23K3 BAC clone fragment (cloned in pCOM32), which complemented the wol mutation. (B) Structure of the WOL gene. Exons are indicated as solid bars. Three combinations of dotted lines show the alternative splicing variations of the WOL gene (deposited in GenBank). All result in the identical longest open reading frame with an ATG in position 13572–13574 of the BAC T23K3. The wol mutation is located in the third exon (asterisk), where it is converting T278 (ACT) to I278 (ATT). The small hatched bar represents the 256-bp probe used in hybridization analyses. (C) Complementation of the wol mutation. Left to right: Cross sections of wol, wol transformed with the pCOM32 construct, and wild-type primary roots. (Arrows) Protoxylem in wild-type and rescued root; (p) pericycle; (pp) sieve elements of protophloem. Scale bar, 30 μm. (D) Predicted domain structure of WOL. Extracellular receptor domain (hatched bar) is located near the N terminus between the two transmembrane regions (vertical solid bars). C-terminal domain consists of a histidine kinase domain (H) and two receiver domains (DA and DB). (E) Amino acid sequence alignment representing a region surrounding the wol mutation site in the putative receptor domain of three WOL-like proteins (WOL, F17L21.11, MXH1.16) and Dictyostelium discoideum DHKA. Identical amino acids are indicated by black boxes. The altered amino acid residue in wol (I278) is shown above the alignment. (F) Northern blot of total RNA from wild-type roots and shoots. Ethidium bromide–stained ribosomal RNA is shown as a loading control.
Figure 4
Figure 4
Localization of WOL mRNA during embryonic and primary root development by in situ hybridization. (A–G) antisense probe. (A) Longitudinal and (B) cross sections of the wild-type primary root. (C) Cross section of wol primary root; (D) globular stage; (E) late heart stage; (F) torpedo stage; (G) bent-cotyledon stage of the wild-type embryo. (H) Torpedo-stage embryo hybridized with a sense WOL probe. Hybridizations of other sections with sense RNA probes did not reveal signals. Scale bar, 50 μm. The endodermal (e) and the innermost ground tissue (g) layer next to the WOL expression domain are indicated.

Similar articles

See all similar articles

Cited by 155 articles

See all "Cited by" articles

Publication types

LinkOut - more resources

Feedback