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| 2. |
- Roberts, Christina Joy, 1983-
(författare)
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Cell-to-Cell Signalling in Arabidopsis Root Development
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Development in multicellular organisms requires a strict balance between cell division and differentiation. The simple architecture of the Arabidopsis thaliana root makes it an ideal model for studying molecular mechanisms controlling both the transition from cell division to cell differentiation and cell fate determination. The class III Homeodomain-Leucine Zipper (HD-ZIP III) transcription factors (TFs) are well known developmental regulators, controlling important aspects of embryogenesis, shoot meristem activity, leaf polarity and vascular patterning. The HD-ZIP III TFs are under post-transcriptional control of microRNA165 (miR165) and miR166. In this thesis, I present a cell-to-cell signalling pathway underlying root vascular patterning and describe signaling pathways downstream of the HD-ZIP III TFs in their control of root development. The TF SHORTROOT (SHR), moves from the vascular stele cells to the surrounding endodermal cell layer. We show that SHR acts here to transcriptionally activate MIR165A and MIR166B, and the miR165/6 produced in the endodermis act non-cell autonomously to post-transcriptionally restrict HD-ZIP III mRNA levels in the peripheral stele. The resulting graded HD-ZIP III activity domain in the radial stele dose-dependently determines vascular cell type; high levels of HD-ZIP III in the central stele result in metaxylem formation while lower levels in the peripheral stele result in protoxylem. We provide evidence that the HD-ZIP III factors act as de novo xylem specifiers, because the quintuple mutant lacking all five HD-ZIP III genes forms no xylem. Furthermore, reducing the plasmodesmatal aperture through callose accumulation inhibits the bi-directional mobility of both signalling molecules, providing evidence that both SHR and miR165/6 move cell-to-cell via plasmodesmata to control root development.I present downstream components of the miR165/HD-ZIP III TFs in the root meristem, identified through a time-course induction of miR165 coupled to transcriptome analyses. This experiment revealed novel roles for HD-ZIP III TFs in vascular patterning and meristem size control. I show that HD-ZIP III directed repression of auxin hormone signalling in the xylem axis is essential for proper xylem differentiation. Furthermore, I provide data to show that they also control the balance of reactive oxygen species in the root meristem, thereby directing meristem size and ultimately controlling root growth.
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| 3. |
- Schlereth, Alexandra, et al.
(författare)
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MONOPTEROS controls embryonic root initiation by regulating a mobile transcription factor
- 2010
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Ingår i: Nature. - : Macmillan Publishers Ltd.. - 0028-0836 .- 1476-4687. ; 464:7290, s. 913-916
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Tidskriftsartikel (refereegranskat)abstract
- Acquisition of cell identity in plants relies strongly on positional information1, hence cell–cell communication and inductive signalling are instrumental for developmental patterning. During Arabidopsis embryogenesis, an extra-embryonic cell is specified to become the founder cell of the primary root meristem, hypophysis, in response to signals from adjacent embryonic cells2. The auxin-dependent transcription factor MONOPTEROS (MP) drives hypophysis specification by promoting transport of the hormone auxin from the embryo to the hypophysis precursor. However, auxin accumulation is not sufficient for hypophysis specification, indicating that additional MP-dependent signals are required3. Here we describe the microarray-based isolation of MP target genes that mediate signalling from embryo to hypophysis. Of three direct transcriptional target genes, TARGET OF MP 5 (TMO5) and TMO7 encode basic helix–loop–helix (bHLH) transcription factors that are expressed in the hypophysis-adjacent embryo cells, and are required and partially sufficient for MP-dependent root initiation. Importantly, the small TMO7 transcription factor moves from its site of synthesis in the embryo to the hypophysis precursor, thus representing a novel MP-dependent intercellular signal in embryonic root specification.
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| 4. |
- Vera-Sirera, Francisco, et al.
(författare)
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A bHLH-Based Feedback Loop Restricts Vascular Cell Proliferation in Plants
- 2015
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Ingår i: Developmental Cell. - : Elsevier BV. - 1534-5807 .- 1878-1551. ; 35:4, s. 432-443
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Tidskriftsartikel (refereegranskat)abstract
- Control of tissue dimensions in multicellular organisms requires the precise quantitative regulation of mitotic activity. In plants, where cells are immobile, tissue size is achieved through control of both cell division orientation and mitotic rate. The bHLH transcription factor heterodimer formed by TARGET OF MONOPTEROS5 (TMO5) and LONESOME HIGHWAY (LHVV) is a central regulator of vascular width-increasing divisions. An important unanswered question is how its activity is limited to specify vascular tissue dimensions. Here we identify a regulatory network that restricts TMO5/LHW activity. We show that thermospermine synthase ACAULIS5 antagonizes TMO5/LHW activity by promoting the accumulation of SAC51-LIKE (SACL) bHLH transcription factors. SACL proteins heterodimerize with LHW therefore likely competing with TMO5/LHW interactions prevent activation of TMO5/LHW target genes, and suppress the over-proliferation caused by excess TMO5/LHW activity. These findings connect two thus-far disparate pathways and provide a mechanistic understanding of the quantitative control of vascular tissue growth.
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