Siobhan Braybrook | University of Cambridge (original) (raw)

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Papers by Siobhan Braybrook

Abstract In a majority of species, leaf development is thought to proceed in a bilaterally symmet... more Abstract In a majority of species, leaf development is thought to proceed in a bilaterally symmetric fashion without systematic asymmetries. This is despite the left and right sides of an initiating primordium occupying niches that differ in their distance from sinks and sources of auxin. Here, we revisit an existing model of auxin transport sufficient to recreate spiral phyllotactic patterns and find previously overlooked asymmetries between auxin distribution and the centers of leaf primordia.

Frontiers in Plant Science, Jan 1, 2012

How is the extensibility of growing plant cell walls regulated? In the past, most studies have fo... more How is the extensibility of growing plant cell walls regulated? In the past, most studies have focused on the role of the cellulose/xyloglucan network and the enigmatic wall-loosening agents expansins. Here we review first how in the closest relatives of the land plants, the Charophycean algae, cell wall synthesis is coupled to cell wall extensibility by a chemical Ca2+-exchange mechanism between Ca2+–pectate complexes. We next discuss evidence for the existence in terrestrial plants of a similar “primitive” Ca2+–pectate-based growth control mechanism in parallel to the more recent, land plant-specific, expansin-dependent process.

Minisymposium 21: Seed Biology

abstracts.aspb.org

The mechanisms that underlie the formation of an embryo are unknown. Higher plants can make embry... more The mechanisms that underlie the formation of an embryo are unknown. Higher plants can make embryos from a variety of cell types: zygotic embryos are the product of gamete fusion, microspores and nucellar tissues can form embryos, and embryos can be induced from somatic ...

Abs# 532: Identification of Target Genes for the Transcription Factor LEAFY COTYLEDON2: Linking Somatic and Zygotic Embryogenesis

abstracts.aspb.org

The mechanisms that underlie the production of an embryo are unknown. We are interested in dissec... more The mechanisms that underlie the production of an embryo are unknown. We are interested in dissecting the molecular networks leading to embryo development by defining the role of the transcription factor LEAFY COTYLEDON2 (LEC2) in inducing somatic embryogenesis. ...

Plant Signaling & …, Jan 1, 2012

Current Biology, Jan 1, 2011

Plant …, Jan 1, 2005

We identified the Arabidopsis (Arabidopsis thaliana) tanmei/emb2757 (tan) mutation that causes de... more We identified the Arabidopsis (Arabidopsis thaliana) tanmei/emb2757 (tan) mutation that causes defects in both embryo and seedling development. tan mutant embryos share many characteristics with the leafy cotyledon (lec) class of mutants in that they accumulate anthocyanin, are intolerant of desiccation, form trichomes on cotyledons, and have reduced accumulation of storage proteins and lipids. Thus, TAN functions both in the early and late phases of embryo development. Moreover, the TAN and LEC genes interact synergistically, suggesting that they do not act in series in the same genetic pathway but, rather, that they have overlapping roles during embryogenesis. tan mutants die as embryos, but immature mutant seeds can be germinated in culture. However, tan mutant seedlings are defective in shoot and root development, their hypocotyls fail to elongate in the dark, and they die as seedlings. We isolated the TAN gene and showed that the predicted polypeptide has seven WD repeat motifs, suggesting that TAN forms complexes with other proteins. Together, these results suggest that TAN interacts with other proteins to control many aspects of embryo development. ; fax 530-752-5410.

Plant Cell, Jan 1, 2010

A leaf develops from a few cells that grow, divide, and differentiate to form a complex organ tha... more A leaf develops from a few cells that grow, divide, and differentiate to form a complex organ that is precisely positioned relative to its neighbors. How cells communicate to achieve such coordinated growth and development is the focus of this review. We discuss (1) how the stem cells within the shoot meristem gain competence to form organs, (2) what determines the positioning and initiation of new organs, and (3) how the new organ attains its characteristic shape and polarity. Special emphasis is given to the recent integration of mathematics and physics in the study of leaf development.

Plant Cell and Environment, Jan 1, 2006

The C-repeat (CRT)-binding factor/dehydration-responsive element (DRE) binding protein 1 (CBF/DRE... more The C-repeat (CRT)-binding factor/dehydration-responsive element (DRE) binding protein 1 (CBF/DREB1) transcription factors control an important pathway for increased freezing and drought tolerance in plants. Three CBF/DREB1-like genes, CBF 1–3, were isolated from both freezing-tolerant wild grape (Vitis riparia) and freezing-sensitive cultivated grape (Vitis vinifera). The deduced proteins in V. riparia are 63–70% identical to each other and 96–98% identical to the corresponding proteins in V. vinifera. All Vitis CBF proteins are 42–51% identical to AtCBF1 and contain CBF-specific amino acid motifs, supporting their identification as CBF proteins. Grape CBF sequences are unique in that they contain 20–29 additional amino acids and three serine stretches. Agro-infiltration experiments revealed that VrCBF1b localizes to the nucleus. VrCBF1a, VrCBF1b and VvCBF1 activated a green fluorescent protein (GFP) or glucuronidase (GUS) reporter gene behind CRT-containing promoters. Expression of the endogenous CBF genes was low at ambient temperature and enhanced upon low temperature (4 °C) treatment, first for CBF1, followed by CBF2, and about 2 d later by CBF3. No obvious significant difference was observed between V. riparia and V. vinifera genes. The expression levels of all three CBF genes were higher in young tissues than in older tissues. CBF1, 2 and 3 transcripts also accumulated in response to drought and exogenous abscisic acid (ABA) treatment, indicating that grape contains unique CBF genes.

Trends in Plant Science, Jan 1, 2008

Two fundamental aspects of plant development are the maturation phase of embryo development in se... more Two fundamental aspects of plant development are the maturation phase of embryo development in seed plants and totipotency via somatic embryogenesis (SE). The LEAFY COTYLEDON (LEC) transcription factors (TFs) establish environments that promote cellular processes characteristic of the maturation phase and the initiation of somatic embryo formation. Based on recent studies, we and others propose that specific target genes activated by the LEC TFs underlie, in part, their roles in the maturation phase and SE. We also propose that the effect of LEC TFs on the balance of abscisic acid to gibberellic acid might link their roles in totipotency and the maturation phase.

Proceedings of the …, Jan 1, 2008

LEAFY COTYLEDON2 (LEC2) is a central regulator of embryogenesis sufficient to induce somatic cell... more LEAFY COTYLEDON2 (LEC2) is a central regulator of embryogenesis sufficient to induce somatic cells to form embryos when expressed ectopically. Here, we analyze the cellular processes induced by LEC2, a B3 domain transcription factor, that may underlie its ability to promote somatic embryogenesis. We show auxin-responsive genes are induced after LEC2 activation in seedlings. Genes encoding enzymes involved in auxin biosynthesis, YUC2 and YUC4, are activated within 1 h after induction of LEC2 activity, and YUC4 appears to be a direct transcriptional target of LEC2. We also show ectopic LEC2 expression induces accumulation of seed storage protein and oil bodies in vegetative and reproductive organs, events that normally occur during the maturation phase of embryogenesis. Furthermore, LEC2 activates seed protein genes before an increase in RNAs encoding LEC1 or FUS3 is observed. Thus, LEC2 causes rapid changes in auxin responses and induces cellular differentiation characteristic of the maturation phase. The relevance of these changes to the ability of LEC2 to promote somatic embryogenesis is discussed. seed development ͉ totipotency A n outstanding characteristic of plants is their totipotency.

Proceedings of The National Academy of Sciences, Jan 1, 2006

The B3 domain protein LEAFY COTYLEDON2 (LEC2) is required for several aspects of embryogenesis, i... more The B3 domain protein LEAFY COTYLEDON2 (LEC2) is required for several aspects of embryogenesis, including the maturation phase, and is sufficient to induce somatic embryo development in vegetative cells. Here, we demonstrate that LEC2 directly controls a transcriptional program involved in the maturation phase of seed development. Induction of LEC2 activity in seedlings causes rapid accumulation of RNAs normally present primarily during the maturation phase. Several RNAs encode proteins with known roles in maturation processes, including seed-storage and lipid-body proteins. Clustering analyses identified other LEC2-induced RNAs not previously shown to be involved in the maturation phase. We show further that genes encoding these maturation RNAs all possess in their 5 flanking regions RY motifs, DNA elements bound by other closely related B3 domain transcription factors. Our finding that recombinant LEC2 specifically binds RY motifs from the 5 flanking regions of LEC2-induced genes provides strong evidence that these genes represent transcriptional targets of LEC2. Although these LEC2-induced RNAs accumulate primarily during the maturation phase, we show that a subset, including AGL15 and IAA30, accumulate in seeds containing zygotes. We discuss how identification of LEC2 target genes provides a potential link between the roles of LEC2 in the maturation phase and in the induction of somatic embryogenesis.

Abstract In a majority of species, leaf development is thought to proceed in a bilaterally symmet... more Abstract In a majority of species, leaf development is thought to proceed in a bilaterally symmetric fashion without systematic asymmetries. This is despite the left and right sides of an initiating primordium occupying niches that differ in their distance from sinks and sources of auxin. Here, we revisit an existing model of auxin transport sufficient to recreate spiral phyllotactic patterns and find previously overlooked asymmetries between auxin distribution and the centers of leaf primordia.

Frontiers in Plant Science, Jan 1, 2012

How is the extensibility of growing plant cell walls regulated? In the past, most studies have fo... more How is the extensibility of growing plant cell walls regulated? In the past, most studies have focused on the role of the cellulose/xyloglucan network and the enigmatic wall-loosening agents expansins. Here we review first how in the closest relatives of the land plants, the Charophycean algae, cell wall synthesis is coupled to cell wall extensibility by a chemical Ca2+-exchange mechanism between Ca2+–pectate complexes. We next discuss evidence for the existence in terrestrial plants of a similar “primitive” Ca2+–pectate-based growth control mechanism in parallel to the more recent, land plant-specific, expansin-dependent process.

Minisymposium 21: Seed Biology

abstracts.aspb.org

The mechanisms that underlie the formation of an embryo are unknown. Higher plants can make embry... more The mechanisms that underlie the formation of an embryo are unknown. Higher plants can make embryos from a variety of cell types: zygotic embryos are the product of gamete fusion, microspores and nucellar tissues can form embryos, and embryos can be induced from somatic ...

Abs# 532: Identification of Target Genes for the Transcription Factor LEAFY COTYLEDON2: Linking Somatic and Zygotic Embryogenesis

abstracts.aspb.org

The mechanisms that underlie the production of an embryo are unknown. We are interested in dissec... more The mechanisms that underlie the production of an embryo are unknown. We are interested in dissecting the molecular networks leading to embryo development by defining the role of the transcription factor LEAFY COTYLEDON2 (LEC2) in inducing somatic embryogenesis. ...

Plant Signaling & …, Jan 1, 2012

Current Biology, Jan 1, 2011

Plant …, Jan 1, 2005

We identified the Arabidopsis (Arabidopsis thaliana) tanmei/emb2757 (tan) mutation that causes de... more We identified the Arabidopsis (Arabidopsis thaliana) tanmei/emb2757 (tan) mutation that causes defects in both embryo and seedling development. tan mutant embryos share many characteristics with the leafy cotyledon (lec) class of mutants in that they accumulate anthocyanin, are intolerant of desiccation, form trichomes on cotyledons, and have reduced accumulation of storage proteins and lipids. Thus, TAN functions both in the early and late phases of embryo development. Moreover, the TAN and LEC genes interact synergistically, suggesting that they do not act in series in the same genetic pathway but, rather, that they have overlapping roles during embryogenesis. tan mutants die as embryos, but immature mutant seeds can be germinated in culture. However, tan mutant seedlings are defective in shoot and root development, their hypocotyls fail to elongate in the dark, and they die as seedlings. We isolated the TAN gene and showed that the predicted polypeptide has seven WD repeat motifs, suggesting that TAN forms complexes with other proteins. Together, these results suggest that TAN interacts with other proteins to control many aspects of embryo development. ; fax 530-752-5410.

Plant Cell, Jan 1, 2010

A leaf develops from a few cells that grow, divide, and differentiate to form a complex organ tha... more A leaf develops from a few cells that grow, divide, and differentiate to form a complex organ that is precisely positioned relative to its neighbors. How cells communicate to achieve such coordinated growth and development is the focus of this review. We discuss (1) how the stem cells within the shoot meristem gain competence to form organs, (2) what determines the positioning and initiation of new organs, and (3) how the new organ attains its characteristic shape and polarity. Special emphasis is given to the recent integration of mathematics and physics in the study of leaf development.

Plant Cell and Environment, Jan 1, 2006

The C-repeat (CRT)-binding factor/dehydration-responsive element (DRE) binding protein 1 (CBF/DRE... more The C-repeat (CRT)-binding factor/dehydration-responsive element (DRE) binding protein 1 (CBF/DREB1) transcription factors control an important pathway for increased freezing and drought tolerance in plants. Three CBF/DREB1-like genes, CBF 1–3, were isolated from both freezing-tolerant wild grape (Vitis riparia) and freezing-sensitive cultivated grape (Vitis vinifera). The deduced proteins in V. riparia are 63–70% identical to each other and 96–98% identical to the corresponding proteins in V. vinifera. All Vitis CBF proteins are 42–51% identical to AtCBF1 and contain CBF-specific amino acid motifs, supporting their identification as CBF proteins. Grape CBF sequences are unique in that they contain 20–29 additional amino acids and three serine stretches. Agro-infiltration experiments revealed that VrCBF1b localizes to the nucleus. VrCBF1a, VrCBF1b and VvCBF1 activated a green fluorescent protein (GFP) or glucuronidase (GUS) reporter gene behind CRT-containing promoters. Expression of the endogenous CBF genes was low at ambient temperature and enhanced upon low temperature (4 °C) treatment, first for CBF1, followed by CBF2, and about 2 d later by CBF3. No obvious significant difference was observed between V. riparia and V. vinifera genes. The expression levels of all three CBF genes were higher in young tissues than in older tissues. CBF1, 2 and 3 transcripts also accumulated in response to drought and exogenous abscisic acid (ABA) treatment, indicating that grape contains unique CBF genes.

Trends in Plant Science, Jan 1, 2008

Two fundamental aspects of plant development are the maturation phase of embryo development in se... more Two fundamental aspects of plant development are the maturation phase of embryo development in seed plants and totipotency via somatic embryogenesis (SE). The LEAFY COTYLEDON (LEC) transcription factors (TFs) establish environments that promote cellular processes characteristic of the maturation phase and the initiation of somatic embryo formation. Based on recent studies, we and others propose that specific target genes activated by the LEC TFs underlie, in part, their roles in the maturation phase and SE. We also propose that the effect of LEC TFs on the balance of abscisic acid to gibberellic acid might link their roles in totipotency and the maturation phase.

Proceedings of the …, Jan 1, 2008

LEAFY COTYLEDON2 (LEC2) is a central regulator of embryogenesis sufficient to induce somatic cell... more LEAFY COTYLEDON2 (LEC2) is a central regulator of embryogenesis sufficient to induce somatic cells to form embryos when expressed ectopically. Here, we analyze the cellular processes induced by LEC2, a B3 domain transcription factor, that may underlie its ability to promote somatic embryogenesis. We show auxin-responsive genes are induced after LEC2 activation in seedlings. Genes encoding enzymes involved in auxin biosynthesis, YUC2 and YUC4, are activated within 1 h after induction of LEC2 activity, and YUC4 appears to be a direct transcriptional target of LEC2. We also show ectopic LEC2 expression induces accumulation of seed storage protein and oil bodies in vegetative and reproductive organs, events that normally occur during the maturation phase of embryogenesis. Furthermore, LEC2 activates seed protein genes before an increase in RNAs encoding LEC1 or FUS3 is observed. Thus, LEC2 causes rapid changes in auxin responses and induces cellular differentiation characteristic of the maturation phase. The relevance of these changes to the ability of LEC2 to promote somatic embryogenesis is discussed. seed development ͉ totipotency A n outstanding characteristic of plants is their totipotency.

Proceedings of The National Academy of Sciences, Jan 1, 2006

The B3 domain protein LEAFY COTYLEDON2 (LEC2) is required for several aspects of embryogenesis, i... more The B3 domain protein LEAFY COTYLEDON2 (LEC2) is required for several aspects of embryogenesis, including the maturation phase, and is sufficient to induce somatic embryo development in vegetative cells. Here, we demonstrate that LEC2 directly controls a transcriptional program involved in the maturation phase of seed development. Induction of LEC2 activity in seedlings causes rapid accumulation of RNAs normally present primarily during the maturation phase. Several RNAs encode proteins with known roles in maturation processes, including seed-storage and lipid-body proteins. Clustering analyses identified other LEC2-induced RNAs not previously shown to be involved in the maturation phase. We show further that genes encoding these maturation RNAs all possess in their 5 flanking regions RY motifs, DNA elements bound by other closely related B3 domain transcription factors. Our finding that recombinant LEC2 specifically binds RY motifs from the 5 flanking regions of LEC2-induced genes provides strong evidence that these genes represent transcriptional targets of LEC2. Although these LEC2-induced RNAs accumulate primarily during the maturation phase, we show that a subset, including AGL15 and IAA30, accumulate in seeds containing zygotes. We discuss how identification of LEC2 target genes provides a potential link between the roles of LEC2 in the maturation phase and in the induction of somatic embryogenesis.