| 1. |
- Augstein, Frauke, et al.
(författare)
-
DELLA-regulated root xylem developmental response to salt stress in Arabidopsis
-
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.
|
|
| 2. |
- Augstein, Frauke, et al.
(författare)
-
Getting to the Roots : A Developmental Genetic View of Root Anatomy and Function From Arabidopsis to Lycophytes
- 2018
-
Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 9
-
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.
|
|
| 3. |
- Augstein, Frauke
(författare)
-
Mechanisms of plant root xylem developmental plasticity in response to water deficiency and salt
- 2022
-
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.
|
|
| 4. |
- Augstein, Frauke, et al.
(författare)
-
Salinity induces discontinuous protoxylem via a DELLA-dependent mechanism promoting salt tolerance in Arabidopsis seedlings
- 2022
-
Ingår i: New Phytologist. - : Wiley-Blackwell. - 0028-646X .- 1469-8137. ; 236:1, s. 195-209
-
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.
|
|
| 5. |
- Blanco-Tourinan, Noel, et al.
(författare)
-
The primary root procambium contributes to lateral root formation through its impact on xylem connection
- 2023
-
Ingår i: Current Biology. - : CELL PRESS. - 0960-9822 .- 1879-0445. ; 33:9, s. 1716-1727
-
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.
|
|
| 6. |
- Carlsbecker, Annelie, 1972-, et al.
(författare)
-
Xylem versus phloem in secondary growth : a balancing act mediated by gibberellins
- 2021
-
Ingår i: Journal of Experimental Botany. - : Oxford University Press (OUP). - 0022-0957 .- 1460-2431. ; 72:10, s. 3489-3492
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Secondary growth generates wood, which constitutes most of the plant biomass. Despite considerable efforts over the last decade to uncover the genetic and molecular regulation of the vascular cambium, there is still much to learn about how it produces wood (xylem) inward and bast (phloem) outward. Ben-Targem et al. (2021) now provide novel insight into how the hormones auxin and gibberellic acid (GA) govern the activity of the cambium, promoting a transition from formation of equal amounts of xylem and phloem to a stage where xylem formation dominates phloem in Arabidopsis hypocotyls, resembling wood formation in trees.
|
|
| 7. |
- Engelsdorf, Timo, et al.
(författare)
-
The plant cell wall integrity maintenance and immune signaling systems cooperate to control stress responses in Arabidopsis thaliana
- 2018
-
Ingår i: Science Signaling. - : American Association for the Advancement of Science (AAAS). - 1945-0877 .- 1937-9145. ; 11:536
-
Tidskriftsartikel (refereegranskat)abstract
- Cell walls surround all plant cells, and their composition and structure are modified in a tightly controlled, adaptive manner to meet sometimes opposing functional requirements during growth and development. The plant cell wall integrity (CWI) maintenance mechanism controls these functional modifications, as well as responses to cell wall damage (CWD). We investigated how the CWI system mediates responses to CWD in Arabidopsis thaliana. CWD induced by cell wall-degrading enzymes or an inhibitor of cellulose biosynthesis elicited similar, turgor-sensitive stress responses. Phenotypic clustering with 27 genotypes identified a core group of receptor-like kinases (RLKs) and ion channels required for the activation of CWD responses. A genetic analysis showed that the RLK FEI2 and the plasma membrane-localized mechanosensitive Ca2+ channel MCA1 functioned downstream of the RLK THE1 in CWD perception. In contrast, pattern-triggered immunity (PTI) signaling components, including the receptors for plant elicitor peptides (AtPeps) PEPR1 and PEPR2, repressed responses to CWD. CWD induced the expression of PROPEP1 and PROPEP3, which encode the precursors of AtPep1 and AtPep3, and the release of PROPEP3 into the growth medium. Application of AtPep1 and AtPep3 repressed CWD-induced phytohormone accumulation in a concentration-dependent manner. These results suggest that AtPep-mediated signaling suppresses CWD-induced defense responses controlled by the CWI mechanism. This suppression was alleviated when PTI signaling downstream of PEPR1 and PEPR2 was impaired. Defense responses controlled by the CWI maintenance mechanism might thus compensate to some extent for the loss of PTI signaling elements.
|
|
| 8. |
- Feng, Ming, et al.
(författare)
-
Plant grafting: Molecular mechanisms and applications
- 2024
-
Ingår i: Molecular Plant. - 1674-2052 .- 1752-9867. ; 17, s. 75-91
-
Forskningsöversikt (refereegranskat)abstract
- People have grafted plants since antiquity for propagation, to increase yields, and to improve stress tolerance. This cutting and joining of tissues activates an incredible regenerative ability as different plants fuse and grow as one. For over a hundred years, people have studied the scientific basis for how plants graft. Today, new techniques and a deepening knowledge of the molecular basis for graft formation have allowed a range of previously ungraftable combinations to emerge. Here, we review recent developments in our understanding of graft formation, including the attachment and vascular formation steps. We analyze why plants graft and how biotic and abiotic factors influence successful grafting. We also discuss the ability and inability of plants to graft, and how grafting has transformed both horticulture and fundamental plant science. As our knowledge about plant grafting improves, new combinations and techniques will emerge to allow an expanded use of grafting for horticultural applications and to address fundamental research questions.
|
|
| 9. |
- Ramachandran, Prashanth, et al.
(författare)
-
Abscisic acid signaling activates distinct VND transcription factors to promote xylem differentiation in Arabidopsis
- 2021
-
Ingår i: Current Biology. - : Cell Press. - 0960-9822 .- 1879-0445. ; 31:14, s. 3153-3161.e5
-
Tidskriftsartikel (refereegranskat)abstract
- Plants display remarkable abilities to adjust growth and development to environmental conditions, such as the amount of available water. This developmental plasticity is apparent not only in root and shoot growth rates, but also in tissue patterning and cell morphology.(1,2) We have previously shown that in response to limited water availability, Arabidopsis thaliana root displays changes in xylem morphology, mediated by the non-cell-autonomous action of abscisic acid, ABA.(2) Here, we show, through analyses of ABA response reporters and tissue-specific suppression of ABA signaling, that xylem cells themselves act as primary signaling centers governing both xylemcell fate and xylem differentiation rate, revealing the cell-autonomous control of multiple aspects of xylem development by ABA. ABA rapidly activates the expression of genes encoding VASCULAR-RELATED NAC DOMAIN (VND) transcription factors. Molecular and genetic analyses revealed that the two ABA-mediated xylem developmental changes are regulated by distinct members of this transcription factor family, with VND2 and VND3 promoting differentiation rate of metaxylem cells, while VND7 promotes the conversion of metaxylem toward protoxylem morphology. This phenomenon shows how different aspects of developmental plasticity can be interlinked, yet genetically separable. Moreover, similarities in phenotypic and molecular responses to ABA in diverse species indicate evolutionary conservation of the ABA-xylem development regulatory network among eudicots. Hence, this study gives molecular insights into how environmental stress modifies plant vascular anatomy and has potential relevance for water use optimization and adaptation to drought conditions.
|
|
| 10. |
- Ramachandran, Prashanth, et al.
(författare)
-
Continuous root xylem formation and vascular acclimation to water deficit involves endodermal ABA signalling via miR165
- 2018
-
Ingår i: Development. - : COMPANY OF BIOLOGISTS LTD. - 0950-1991 .- 1477-9129. ; 145:3
-
Tidskriftsartikel (refereegranskat)abstract
- The plant root xylem comprises a specialized tissue for water distribution to the shoot. Despite its importance, its potential morphological plasticity in response to environmental conditions such as limited water availability has not been thoroughly studied. Here, we identify a role for the phytohormone abscisic acid (ABA) for proper xylem development and describe how ABA signalling-mediated effects on core developmental regulators are employed to alter xylem morphology under limited water availability in Arabidopsis. Plants with impaired ABA biosynthesis and reduced ABA signalling in the cell layer surrounding the vasculature displayed defects in xylem continuity, suggesting that non-cell autonomous ABA signalling is required for proper xylem development. Conversely, upon external ABA application or under limited water availability, extra xylem strands were formed. The observed xylem developmental alterations were dependent on adequate endodermal ABA signalling, which activated MIR165A. This resulted in increased miR165 levels that repress class III HD-ZIP transcription factors in the stele. We conclude that a pathway known to control core developmental features is employed as a means of modifying plant xylem morphology under conditions of environmental stress.
|
|
