| 1. |
- Augstein, Frauke, et al.
(författare)
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DELLA-regulated root xylem developmental response to salt stress in Arabidopsis
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Salinity impairs plant growth and leads to reduction in yield in many crop species. Salt reduces water availability and exposes the plant to ion toxicity. However, plants exhibit an incredible developmental plasticity to adjust to environmental stresses, and xylem development can respond to water limitation with enhanced xylem differentiation rates and alterations in xylem cell morphology. Here, we report that salinity triggers a distinct response, with the formation of discontinuous protoxylem, protoxylem gaps, in Arabidopsis seedlings. The formation of protoxylem gaps may confer enhanced tolerance to salt, as mutants exhibiting more protoxylem gaps survive salt stress better, while mutants not forming xylem gaps are less tolerant. We present results suggesting that salt induces protoxylem gaps as a consequence of reduced gibberellin levels and signaling, and protoxylem gap formation is suppressed in the della quintuple mutant, in which GA signaling is no longer under DELLA repression. Transcriptome analysis upon salt stress in the della quintuple mutant revealed a previously unknown role for the xylem master regulator VASCULAR RELATED NAC DOMAIN 6 (VND6) in protoxylem gap formation. With VND6 several factors involved in secondary cell wall formation or cell wall modification were differentially expressed upon salt, including several alfa expansins. Seedlings of both salt sensitive and salt tolerant eudicot species form protoxylem gaps upon salt stress, suggesting that this response is conserved among eudicot species.
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| 2. |
- Augstein, Frauke, et al.
(författare)
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Getting to the Roots : A Developmental Genetic View of Root Anatomy and Function From Arabidopsis to Lycophytes
- 2018
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Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 9
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Forskningsöversikt (refereegranskat)abstract
- Roots attach plants to the ground and ensure efficient and selective uptake of water and nutrients. These functions are facilitated by the morphological and anatomical structures of the root, formed by the activity of the root apical meristem (RAM) and consecutive patterning and differentiation of specific tissues with distinct functions. Despite the importance of this plant organ, its evolutionary history is not clear, but fossils suggest that roots evolved at least twice, in the lycophyte (clubmosses and their allies) and in the euphyllophyte (ferns and seed plants) lineages. Both lycophyte and euphyllophyte roots grow indeterminately by the action of an apical meristem, which is protected by a root cap. They produce root hairs, and in most species the vascular stele is guarded by a specialized endodermal cell layer. Hence, most of these traits must have evolved independently in these lineages. This raises the question if the development of these apparently analogous tissues is regulated by distinct or homologous genes, independently recruited from a common ancestor of lycophytes and euphyllophytes. Currently, there are few studies of the genetic and molecular regulation of lycophyte and fern roots. Therefore, in this review, we focus on key regulatory networks that operate in root development in the model angiosperm Arabidopsis. We describe current knowledge of the mechanisms governing RAM maintenance as well as patterning and differentiation of tissues, such as the endodermis and the vasculature, and compare with other species. We discuss the importance of comparative analyses of anatomy and morphology of extant and extinct species, along with analyses of gene regulatory networks and, ultimately, gene function in plants holding key phylogenetic positions to test hypotheses of root evolution.
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| 3. |
- Augstein, Frauke
(författare)
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Mechanisms of plant root xylem developmental plasticity in response to water deficiency and salt
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plants may be exposed to a variety of different environmental conditions including water deficiency and salt, both affecting the uptake of water into the plant. Water is taken up from the soil by the roots and distributed throughout the plant via the water conducting tissue, the xylem. Plants are remarkably plastic and have evolved different mechanisms to sense the environment and adjust their development accordingly. However, how xylem development may respond to water availability is not clear. In this thesis, I show how water deficiency and salt affect xylem development and how the observed phenotypic alterations are regulated on a molecular level. We found that upon water deficiency additional protoxylem strands were formed along with an early differentiation of the inner metaxylem. These phenotypes were regulated both by non-cell autonomous and cell autonomous signaling via the hormone abscisic acid (ABA). The expression of microRNA165 was induced by ABA signaling in the endodermis leading to downregulation of homeo domain leucine zipper class III (HD-ZIP III) transcription factors in the stele. This caused a shift in xylem identity from meta- to protoxylem and the formation of additional protoxylem strands. At the same time, cell autonomous ABA signaling upregulated several VASCULAR RELATED NAC DOMAIN (VND) transcription factors including VND7, which promoted the shift in xylem identity as well as VND2 and VND3, which promoted early differentiation of the inner metaxylem. In contrast, during an initial phase of salt stress, we observed the formation of protoxylem gaps specifically in response to ionic stress and distinct from ABA-signaling. We identified that protoxylem gaps were caused by lowered levels and signaling of the growth regulator gibberellin (GA). Downstream of GA-signaling, protoxylem gap formation upon salt was controlled by genes involved in secondary cell wall formation including the xylem master regulator VND6 and factors involved in cell wall modification. Salt tolerance assays suggested that protoxylem gaps may contribute to salt tolerance and the phenotypes that we observed upon water deficiency have been suggested to confer drought tolerance. We observed similar effects on xylem developmental plasticity in response to water deficiency and salt in various different dicot species indicating an evolutionary conservation. Thus, xylem development is of high relevance for breeding programs to generate plant varieties better adapted to a changing climate.
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| 4. |
- Augstein, Frauke, et al.
(författare)
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Salinity induces discontinuous protoxylem via a DELLA-dependent mechanism promoting salt tolerance in Arabidopsis seedlings
- 2022
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Ingår i: New Phytologist. - : Wiley-Blackwell. - 0028-646X .- 1469-8137. ; 236:1, s. 195-209
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Tidskriftsartikel (refereegranskat)abstract
- Salinity is detrimental to plants and developmental adjustments limiting salt uptake and transport is therefore important for acclimation to high salt. These parameters may be influenced by xylem morphology, however how plant root xylem development is affected by salt stress remains unclear.Using molecular and genetic techniques and detailed phenotypic analyses, we demonstrate that salt causes distinct effects on Arabidopsis seedling root xylem and reveal underlying molecular mechanisms.Salinity causes intermittent inhibition of protoxylem cell differentiation, generating protoxylem gaps, in Arabidopsis and several other eudicot seedlings. The extent of protoxylem gaps in seedlings positively correlates with salt tolerance. Reduced gibberellin signalling is required for protoxylem gap formation. Mutant analyses reveal that the xylem differentiation regulator VASCULAR RELATED NAC DOMAIN 6 (VND6), along with secondary cell wall producing and cell wall modifying enzymes, including EXPANSIN A1 (EXP1), are involved in protoxylem gap formation, in a DELLA-dependent manner.Salt stress is likely to reduce levels of bioactive gibberellins, stabilising DELLAs, which in turn activates multiple factors modifying protoxylem differentiation. Salt stress impacts seedling survival and formation of protoxylem gaps may be a measure to enhance salt tolerance.
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| 5. |
- Blanco-Tourinan, Noel, et al.
(författare)
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The primary root procambium contributes to lateral root formation through its impact on xylem connection
- 2023
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Ingår i: Current Biology. - : CELL PRESS. - 0960-9822 .- 1879-0445. ; 33:9, s. 1716-1727
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Tidskriftsartikel (refereegranskat)abstract
- The postembryonic formation of lateral roots (LRs) starts in internal root tissue, the pericycle. An important question of LR development is how the connection of the primary root vasculature with that of the emerging LR is established and whether the pericycle and/or other cell types direct this process. Here, using clonal analysis and time-lapse experiments, we show that both the procambium and pericycle of the primary root (PR) affect the LR vascular connectivity in a coordinated manner. We show that during LR formation, pro -cambial derivates switch their identity and become precursors of xylem cells. These cells, together with the pericycle-origin xylem, participate in the formation of what we call a "xylem bridge"(XB), which establishes the xylem connection between the PR and the nascent LR. If the parental protoxylem cell fails to differentiate, XB is still sometimes formed but via a connection with metaxylem cells, highlighting that this process has some plasticity. Using mutant analyses, we show that the early specification of XB cells is determined by CLASS III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) transcription factors (TFs). Subsequent XB cell dif-ferentiation is marked by the deposition of secondary cell walls (SCWs) in spiral and reticulate/scalariform patterns, which is dependent on the VASCULAR-RELATED NAC-DOMAIN (VND) TFs. XB elements were also observed in Solanum lycopersicum, suggesting that this mechanism may be more widely conserved in plants. Together, our results suggest that plants maintain vascular procambium activity, which safeguards the functionality of newly established lateral organs by assuring the continuity of the xylem strands throughout the root system.
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| 6. |
- Blaschek, Leonard
(författare)
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Cellular Lignin Distribution Patterns and their Physiological Relevance
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The diverse morphological shapes of plants are made possible by the structural rigidity provided by cell walls. In order to support vertical growth and long distance water transport, cell walls need to resist a variety of biological and physical stresses. Lignin, a cell wall polyphenolic unique to vascular plants, has long been considered to structurally support the cell walls of xylem vessels and other specialised cell types against these forces. Lignin is a complex polymer whose monomeric composition and biochemical properties vary widely between different species, tissues and cell types. However, the precise characterisation of this micro-scale variation poses considerable methodological hurdles. As a result, it has yet to be understood how differences in lignin composition contribute to the cell-type specific functions of the cell wall. In the works presented herein, we optimise and validate the Wiesner test and Raman microspectroscopy for the quantitative characterisation of lignin in situ and use these techniques to show how cell-type specific genetic regulation of lignification is crucial for cell wall function. Using synthetic lignin monomers and polymers, as well as genetically altered Arabidopsis and Populus plants in conjunction with biochemical lignin composition analyses, we establish the Wiesner test as a specific high-resolution method to quantify coniferaldehyde (I), and show that Raman microspectroscopy allows the relative quantification of total lignin, guaiacyl lignin subunits (G-units), coniferyl alcohol and syringyl lignin subunits (S-units) (II). We then use these methods to characterise cell-autonomous and cell-cell cooperative lignification patterns and show that cell walls of different vessel types depend on distinct amounts of lignin and specific G-units for structural reinforcement (III). S-unit incorporation into vessel lignin and increased adjacency to neighbouring vessels on the other hand compromise their resistance to collapse (III). Altogether, we provide evidence for a lignification process consisting of a fine scale, cell-type specific regulatory network of lignin biosynthesis, cell-to-cell cooperative monomer supply, and cell wall layer specific monomer incorporation. Crucially, it is this dynamic small-scale regulation that allows lignified plant cell walls to fulfil their cell-type specific functions.
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| 7. |
- Carlsbecker, Annelie, et al.
(författare)
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Cell signalling by microRNA165/6 directs gene dose-dependent root cell fate
- 2010
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 465:7296, s. 316-321
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Tidskriftsartikel (refereegranskat)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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| 8. |
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| 9. |
- Carlsbecker, Annelie, 1972-
(författare)
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MADS-Box Gene Phylogeny and the Evolution of Plant Form : Characterisation of a Family of Regulators of Reproductive Development from the Conifer Norway Spruce, Picea abies
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The evolutionary relationships between the angiosperm floral organs and the reproductive organs of other seed plants is not known. Flower organ development requires transcription factors encoded by the MADS-box genes. Since the evolution of novel morphology likely involve changes in developmental regulators, I have analysed MADS-box genes from the conifer Norway spruce, Picea abies, a representative of the gymnosperm group of seed plants.The results show that the MADS-box gene family has evolved via gene duplications and subsequent diversifications in correlation in time with the evolution of morphological novelties along the seed-plant lineage.Angiosperm MADS-box genes that determine petal and stamen development have homologues in the conifers, that are specifically active in pollen cones. It is, therefore, likely that the common ancestor of these genes controlled the development of the pollen-bearing organs in the early seed plants, and later were recruited for petal development in the angiosperms.Norway spruce set cones at an age of 15-20 years. One of the spruce MADS-box genes analysed may have a function in the control of the transition to reproductive phase, supported by expression data and the effect of the gene on development of transgenic Arabidopsis plants.Two of the spruce genes identified are not closely related to any known angiosperm gene. These may have roles in gymnosperm-specific developmental processes, possibly in the patterning of the conifer cones, as suggested by their expression patterns.The molecular regulation of cone- and flower development in fundamental aspects is highly conserved between conifers and angiosperms, however, differences detected may be informative regarding the origin of morphological complexity.
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| 10. |
- Carlsbecker, Annelie, et al.
(författare)
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Molecular control of normal and acrocona mutant seed cone development in Norway spruce (Picea abies) and the evolution of conifer ovule-bearing organs
- 2013
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 200:1, s. 261-275
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Tidskriftsartikel (refereegranskat)abstract
- Reproductive organs in seed plants are morphologically divergent and their evolutionary history is often unclear. The mechanisms controlling their development have been extensively studied in angiosperms but are poorly understood in conifers and other gymnosperms. Here, we address the molecular control of seed cone development in Norway spruce, Picea abies. We present expression analyses of five novel MADS-box genes in comparison with previously identified MADS and LEAFY genes at distinct developmental stages. In addition, we have characterized the homeotic transformation from vegetative shoot to female cone and associated changes in regulatory gene expression patterns occurring in the acrocona mutant. The analyses identified genes active at the onset of ovuliferous and ovule development and identified expression patterns marking distinct domains of the ovuliferous scale. The reproductive transformation in acrocona involves the activation of all tested genes normally active in early cone development, except for an AGAMOUS-LIKE6/SEPALLATA (AGL6/SEP) homologue. This absence may be functionally associated with the nondeterminate development of the acrocona ovule-bearing scales. Our morphological and gene expression analyses give support to the hypothesis that the modern cone is a complex structure, and the ovuliferous scale the result of reductions and compactions of an ovule-bearing axillary short shoot in cones of Paleozoic conifers.
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