| 1. |
- Carlsbecker, Annelie, et al.
(author)
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Cell signalling by microRNA165/6 directs gene dose-dependent root cell fate
- 2010
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 465:7296, s. 316-321
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Journal article (peer-reviewed)abstract
- A key question in developmental biology is how cells exchange positional information for proper patterning during organ development. In plant roots the radial tissue organization is highly conserved with a central vascular cylinder in which two water conducting cell types, protoxylem and metaxylem, are patterned centripetally. We show that this patterning occurs through crosstalk between the vascular cylinder and the surrounding endodermis mediated by cell-to-cell movement of a transcription factor in one direction and microRNAs in the other. SHORT ROOT, produced in the vascular cylinder, moves into the endodermis to activate SCARECROW. Together these transcription factors activate MIR165a and MIR166b. Endodermally produced microRNA165/6 then acts to degrade its target mRNAs encoding class III homeodomain-leucine zipper transcription factors in the endodermis and stele periphery. The resulting differential distribution of target mRNA in the vascular cylinder determines xylem cell types in a dosage-dependent manner.
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| 2. |
- Cruz-Ramírez, Alfredo, et al.
(author)
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A Bistable Circuit Involving SCARECROW-RETINOBLASTOMA Integrates Cues to Inform Asymmetric Stem Cell Division
- 2012
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In: Cell. - : Elsevier. - 0092-8674 .- 1097-4172. ; 150:5, s. 1002-1015
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Journal article (peer-reviewed)abstract
- In plants, where cells cannot migrate, asymmetric cell divisions (ACDs) must be confined to the appropriate spatial context. We investigate tissue-generating asymmetric divisions in a stem cell daughter within the Arabidopsis root. Spatial restriction of these divisions requires physical binding of the stem cell regulator SCARECROW (SCR) by the RETINOBLASTOM-RELATED (RBR) protein. In the stem cell niche, SCR activity is counteracted by phosphorylation of RBR through a cyclinD6;1-CDK complex. This cyclin is itself under transcriptional control of SCR and its partner SHORT ROOT (SHR), creating a robust bistable circuit with either high or low SHR-SCR complex activity. Auxin biases this circuit by promoting CYCD6;1 transcription. Mathematical modeling shows that ACDs are only switched on after integration of radial and longitudinal information, determined by SHR and auxin distribution, respectively. Coupling of cell-cycle progression to protein degradation resets the circuit, resulting in a "flip flop" that constrains asymmetric cell division to the stem cell region.
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| 3. |
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| 4. |
- Petersson, Sara, et al.
(author)
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An auxin gradient and maximum in the arabidopsis root apex shown by high-resolution cell-specific analysis of IAA distribution and synthesis
- 2009
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In: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 21:6, s. 1659-1668
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Journal article (peer-reviewed)abstract
- Local concentration gradients of the plant growth regulator auxin (indole-3-acetic acid [IAA]) are thought to instruct the positioning of organ primordia and stem cell niches and to direct cell division, expansion, and differentiation. High-resolution measurements of endogenous IAA concentrations in support of the gradient hypothesis are required to substantiate this hypothesis. Here, we introduce fluorescence-activated cell sorting of green fluorescent protein-marked cell types combined with highly sensitive mass spectrometry methods as a novel means for analyses of IAA distribution and metabolism at cellular resolution. Our results reveal the presence of IAA concentration gradients within the Arabidopsis thaliana root tip with a distinct maximum in the organizing quiescent center of the root apex. We also demonstrate that the root apex provides an important source of IAA and that cells of all types display a high synthesis capacity, suggesting a substantial contribution of local biosynthesis to auxin homeostasis in the root tip. Our results indicate that local biosynthesis and polar transport combine to produce auxin gradients and maxima in the root tip.
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| 5. |
- Swarup, Kamal, et al.
(author)
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The auxin influx carrier LAX3 promotes lateral root emergence
- 2008
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In: Nature Cell Biology. - : Nature Publishing Group. - 1465-7392 .- 1476-4679. ; 10:8, s. 946-954
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Journal article (peer-reviewed)abstract
- Lateral roots originate deep within the parental root from a small number of founder cells at the periphery of vascular tissues and must emerge through intervening layers of tissues. We describe how the hormone auxin, which originates from the developing lateral root, acts as a local inductive signal which re-programmes adjacent cells. Auxin induces the expression of a previously uncharacterized auxin influx carrier LAX3 in cortical and epidermal cells directly overlaying new primordia. Increased LAX3 activity reinforces the auxin-dependent induction of a selection of cell-wall-remodelling enzymes, which are likely to promote cell separation in advance of developing lateral root primordia.
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