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Ben Scheres

Publications and source records attributed to Ben Scheres.

At least 19 recordsLinked to original sources
PubMed2006

Vectorial information for Arabidopsis planar polarity is mediated by combined AUX1, EIN2, and GNOM activity.

Cell polarity is commonly coordinated within the plane of a single tissue layer (planar polarity), and hair positioning has been exploited as a simple marker for planar polarization of animal epithelia . The root epidermis of the plant Arabidopsis similarly reveals planar polarity of hair localization close to root tip-oriented (basal) ends of hair-forming cells . Hair position is directed toward a concentration maximum of the hormone auxin in the root tip , but mechanisms driving this plant-specific planar polarity remain elusive. Here, we report that combinatorial action of the auxin influx carrier AUX1, ETHYLENE-INSENSITIVE2 (EIN2) , and GNOM genes mediates the vector for coordinate hair positioning. In aux1;ein2;gnom eb triple mutant roots, hairs display axial (apical or basal) instead of coordinate polar (basal) position, and recruitment of Rho-of-Plant (ROP) GTPases to the hair initiation site reveals the same polar-to-axial switch. The auxin concentration gradient is virtually abolished in aux1;ein2;gnom eb roots, where locally applied auxin can coordinate hair positioning. Moreover, auxin overproduction in sectors of wild-type roots enhances planar ROP and hair polarity over long and short distances. Hence, auxin may provide vectorial information for planar polarity that requires combinatorial AUX1, EIN2, and GNOM activity upstream of ROP positioning.

Arabidopsis↗
PubMed2006

Non-cell-autonomous rescue of anaphase-promoting complex function revealed by mosaic analysis of HOBBIT, an Arabidopsis CDC27 homolog.

The Arabidopsis HOBBIT (HBT) gene encodes a homolog of the CDC27 anaphase-promoting complex/cyclosome subunit and is essential for postembryonic development. We induced loss-of-function clones by Cre/lox-mediated recombination of a single complementing HBT transgene in a background homozygous for the strong mutant allele hbt(2311). Defects in cell division and cell expansion are the primary consequences of ubiquitous postembryonic HBT excision. In roots, both cell division and cell expansion are rapidly affected. In contrast, in leaf primordia, cell division and cell expansion halt after a lag phase, which results in different severities of defects in the proximodistal and mediolateral axes. Surprisingly, small clones reveal non-cell-autonomous rescue of hbt mutant cells, indicating a previously unrecognized compensation mechanism for reduced activity of an anaphase-promoting complex/cyclosome component critical for cell cycle progression.

Anaphase-Promoting Complex-Cyclosome↗
PubMed2006

Whole-genome analysis of the SHORT-ROOT developmental pathway in Arabidopsis.

Stem cell function during organogenesis is a key issue in developmental biology. The transcription factor SHORT-ROOT (SHR) is a critical component in a developmental pathway regulating both the specification of the root stem cell niche and the differentiation potential of a subset of stem cells in the Arabidopsis root. To obtain a comprehensive view of the SHR pathway, we used a statistical method called meta-analysis to combine the results of several microarray experiments measuring the changes in global expression profiles after modulating SHR activity. Meta-analysis was first used to identify the direct targets of SHR by combining results from an inducible form of SHR driven by its endogenous promoter, ectopic expression, followed by cell sorting and comparisons of mutant to wild-type roots. Eight putative direct targets of SHR were identified, all with expression patterns encompassing subsets of the native SHR expression domain. Further evidence for direct regulation by SHR came from binding of SHR in vivo to the promoter regions of four of the eight putative targets. A new role for SHR in the vascular cylinder was predicted from the expression pattern of several direct targets and confirmed with independent markers. The meta-analysis approach was then used to perform a global survey of the SHR indirect targets. Our analysis suggests that the SHR pathway regulates root development not only through a large transcription regulatory network but also through hormonal pathways and signaling pathways using receptor-like kinases. Taken together, our results not only identify the first nodes in the SHR pathway and a new function for SHR in the development of the vascular tissue but also reveal the global architecture of this developmental pathway.

Arabidopsis↗
PubMed2006

Polar PIN localization directs auxin flow in plants.

Polar flow of the phytohormone auxin requires plasma membrane-associated PIN proteins and underlies multiple developmental processes in plants. Here we address the importance of the polarity of subcellular PIN localization for the directionality of auxin transport in Arabidopsis thaliana. Expression of different PINs in the root epidermis revealed the importance of PIN polar positions for directional auxin flow and root gravitropic growth. Interfering with sequence-embedded polarity signals directly demonstrates that PIN polarity is a primary factor in determining the direction of auxin flow in meristematic tissues. This finding provides a crucial piece in the puzzle of how auxin flow can be redirected via rapid changes in PIN polarity.

Arabidopsis↗
PubMed2006

A molecular framework for plant regeneration.

Plants and some animals have a profound capacity to regenerate organs from adult tissues. Molecular mechanisms for regeneration have, however, been largely unexplored. Here we investigate a local regeneration response in Arabidopsis roots. Laser-induced wounding disrupts the flow of auxin-a cell-fate-instructive plant hormone-in root tips, and we demonstrate that resulting cell-fate changes require the PLETHORA, SHORTROOT, and SCARECROW transcription factors. These transcription factors regulate the expression and polar position of PIN auxin efflux-facilitating membrane proteins to reconstitute auxin transport in renewed root tips. Thus, a regeneration mechanism using embryonic root stem-cell patterning factors first responds to and subsequently stabilizes a new hormone distribution.

Arabidopsis↗
PubMed2006

Time-lapse analysis of stem-cell divisions in the Arabidopsis thaliana root meristem.

In the Arabidopsis root, asymmetric stem-cell divisions produce daughters that form the different root cell types. Here we report the establishment of a confocal tracking system that allows the analysis of numbers and orientations of cell divisions in root stem cells. The system provides direct evidence that stem cells have lower division rates than cells in the proximal meristem. It also allows tracking of cell division timing, which we have used to analyse the synchronization of root cap divisions. Finally, it gives new insights into lateral root cap formation: epidermal stem-cell daughters can rotate the orientation of the division plane like the stem cell.

Arabidopsis↗
PubMed2005

The RETINOBLASTOMA-RELATED gene regulates stem cell maintenance in Arabidopsis roots.

The maintenance of stem cells in defined locations is crucial for all multicellular organisms. Although intrinsic factors and signals for stem cell fate have been identified in several species, it has remained unclear how these connect to the ability to reenter the cell cycle that is one of the defining properties of stem cells. We show that local reduction of expression of the RETINOBLASTOMA-RELATED (RBR) gene in Arabidopsis roots increases the amount of stem cells without affecting cell cycle duration in mitotically active cells. Conversely, induced RBR overexpression dissipates stem cells prior to arresting other mitotic cells. Overexpression of D cyclins, KIP-related proteins, and E2F factors also affects root stem cell pool size, and genetic interactions suggest that these factors function in a canonical RBR pathway to regulate somatic stem cells. Expression analysis and genetic interactions position RBR-mediated regulation of the stem cell state downstream of the patterning gene SCARECROW.

Arabidopsis↗
PubMed2005

Cell polarity: ROPing the ends together.

Cell polarity plays an important role in plant development, but the mechanisms that first establish polarity cues remain obscure. By contrast, a flurry of information has recently emerged on the elaboration of cell shape from such unknown initial cell-polarity cues. Recent studies suggest that Rho-related GTPases in plants (ROPs), and their effector targets among the ROP-interactive CRIB motif-containing proteins (RICs), mediate two antagonistic pathways that have opposing action on cell polarization. ROP proteins appear to interact directly with upstream regulators of the ARP2/3 complex, which are conserved modulators of the actin cytoskeleton. ROP function is dependent on the class 1 ADP-ribosylation factors (ARFs), which are core components of the vesicle transport machinery that are also involved in the polar localization of PIN-FORMED (PIN) family auxin efflux facilitators.

ADP-Ribosylation Factors↗
PubMed2005

Stem cells: a plant biology perspective.

A recent meeting at the Juan March Foundation in Madrid, Spain brought together plant biologists to discuss the characteristics of plant stem cells that are unique and those that are shared by stem cells from the animal kingdom.

Animals↗
PubMed2005

Dissection of Arabidopsis ADP-RIBOSYLATION FACTOR 1 function in epidermal cell polarity.

Vesicle trafficking is essential for the generation of asymmetries, which are central to multicellular development. Core components of the vesicle transport machinery, such as ADP-ribosylation factor (ARF) GTPases, have been studied primarily at the single-cell level. Here, we analyze developmental functions of the ARF1 subclass of the Arabidopsis thaliana multigene ARF family. Six virtually identical ARF1 genes are ubiquitously expressed, and single loss-of-function mutants in these genes reveal no obvious developmental phenotypes. Fluorescence colocalization studies reveal that ARF1 is localized to the Golgi apparatus and endocytic organelles in both onion (Allium cepa) and Arabidopsis cells. Apical-basal polarity of epidermal cells, reflected by the position of root hair outgrowth, is affected when ARF1 mutants are expressed at early stages of cell differentiation but after they exit mitosis. Genetic interactions during root hair tip growth and localization suggest that the ROP2 protein is a target of ARF1 action, but its localization is slowly affected upon ARF1 manipulation when compared with that of Golgi and endocytic markers. Localization of a second potential target of ARF1 action, PIN2, is also affected with slow kinetics. Although extreme redundancy precludes conventional genetic dissection of ARF1 functions, our approach separates different ARF1 downstream networks involved in local and specific aspects of cell polarity.

Arabidopsis↗
PubMed2005

The PIN auxin efflux facilitator network controls growth and patterning in Arabidopsis roots.

Local accumulation of the plant growth regulator auxin mediates pattern formation in Arabidopsis roots and influences outgrowth and development of lateral root- and shoot-derived primordia. However, it has remained unclear how auxin can simultaneously regulate patterning and organ outgrowth and how its distribution is stabilized in a primordium-specific manner. Here we show that five PIN genes collectively control auxin distribution to regulate cell division and cell expansion in the primary root. Furthermore, the joint action of these genes has an important role in pattern formation by focusing the auxin maximum and restricting the expression domain of PLETHORA (PLT) genes, major determinants for root stem cell specification. In turn, PLT genes are required for PIN gene transcription to stabilize the auxin maximum at the distal root tip. Our data reveal an interaction network of auxin transport facilitators and root fate determinants that control patterning and growth of the root primordium.

Arabidopsis↗
PubMed2004

The PLETHORA genes mediate patterning of the Arabidopsis root stem cell niche.

A small organizing center, the quiescent center (QC), maintains stem cells in the Arabidopsis root and defines the stem cell niche. The phytohormone auxin influences the position of this niche by an unknown mechanism. Here, we identify the PLETHORA1 (PLT1) and PLT2 genes encoding AP2 class putative transcription factors, which are essential for QC specification and stem cell activity. The PLT genes are transcribed in response to auxin accumulation and are dependent on auxin response transcription factors. Distal PLT transcript accumulation creates an overlap with the radial expression domains of SHORT-ROOT and SCARECROW, providing positional information for the stem cell niche. Furthermore, the PLT genes are activated in the basal embryo region that gives rise to hypocotyl, root, and root stem cells and, when ectopically expressed, transform apical regions to these identities. Thus, the PLT genes are key effectors for establishment of the stem cell niche during embryonic pattern formation.

Arabidopsis↗
PubMed2004

Mosaic analyses using marked activation and deletion clones dissect Arabidopsis SCARECROW action in asymmetric cell division.

In the Arabidopsis root meristem, ground tissue stem cell daughters perform an asymmetric division to form endodermis and cortex. The putative transcription factors SCARECROW (SCR) and SHORTROOT (SHR) regulate this radial patterning event, and the mixed cell fate in scr mutants suggests an atypical role of the SCR gene in asymmetric cell division. Here we use a newly developed site-specific gene activation/deletion system in which induced clones are positively marked with green fluorescent protein (GFP). Using this system, we show that SCR acts cell-autonomously to control asymmetric cell division within the ground tissue. We provide evidence that SCR gene expression is under autoregulatory control, that SCR limits SHR movement, and that transient SCR action is sufficient to separate endodermis and cortex fates by asymmetric cell division.

Arabidopsis↗
PubMed2004

Root genomics: towards digital in situ hybridization.

Separation of cell types and developmental stages in the Arabidopsis root and subsequent expression profiling have yielded a valuable dataset that can be used to select candidate genes for detailed study and to start probing the complexities of gene regulation in plant development.

Computers↗
PubMed2004

Mechanisms of pattern formation in plant embryogenesis.

Many of the patterning mechanisms in plants were discovered while studying postembryonic processes and resemble mechanisms operating during animal development. The emergent role of the plant hormone auxin, however, seems to represent a plant-specific solution to multicellular patterning. This review summarizes our knowledge on how diverse mechanisms that were first dissected at the postembryonic level are now beginning to provide an understanding of plant embryogenesis.

Animals↗
PubMed2003

The Arabidopsis anaphase-promoting complex or cyclosome: molecular and genetic characterization of the APC2 subunit.

In yeast and animals, the anaphase-promoting complex or cyclosome (APC/C) is an essential ubiquitin protein ligase that regulates mitotic progression and exit by controlling the stability of cell cycle regulatory proteins, such as securin and the mitotic cyclins. In plants, the function, regulation, and substrates of the APC/C are poorly understood. To gain more insight into the roles of the plant APC/C, we characterized at the molecular level one of its subunits, APC2, which is encoded by a single-copy gene in Arabidopsis. We show that the Arabidopsis gene is able to partially complement a budding yeast apc2 ts mutant. By yeast two-hybrid assays, we demonstrate an interaction of APC2 with two other APC/C subunits: APC11 and APC8/CDC23. A reverse-genetic approach identified Arabidopsis plants carrying T-DNA insertions in the APC2 gene. apc2 null mutants are impaired in female megagametogenesis and accumulate a cyclin-beta-glucuronidase reporter protein but do not display metaphase arrest, as observed in other systems. The APC2 gene is expressed in various plant organs and does not seem to be cell cycle regulated. Finally, we report intriguing differences in APC2 protein subcellular localization compared with that in other systems. Our observations support a conserved function of the APC/C in plants but a different mode of regulation.

Amino Acid Sequence↗