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Epigenetic Regulation of Light and Hormonal Signaling in Arabidopsis thaliana
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Physiological Botany.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Epigenetisk reglering av ljus och hormon signalering i Arabidopsis thaliana (Swedish)
Abstract [en]

Plants are stationary and need to adapt to the environment they live in. Integration of environmental cues, such as changes in light and temperature, can occur either directly or through the action of hormones. Hormone and light signaling leads to rapid changes in gene expression, and eventually changes in protein levels. In this thesis I have studied how the epigenetic regulator TERMINAL FLOWER2 (TFL2) is involved in light and hormonal signaling in the model organism Arabidopsis thaliana (thale cress). TFL2 is the only Arabidopsis homologue of HETEROCHROMATIN PROTEIN1 (HP1). HP1 proteins have been shown to be involved in repressing gene expression by maintaining the tight structure of heterochromatin or by forming a heterochromatin like structure in euchromatic regions. Unlike metazoan HP1 which can be localized both to eu- and heterochromatin, TFL2 is uniquely localized to euchromatin.

tfl2 mutants have reduced levels of free auxin and a reduced rate of auxin biosynthesis. TFL2 binds to and promotes spatial and temporal expression of the genes belonging to the YUCCA gene family, which are believed to regulate a rate limiting step in the auxin biosynthesis pathway. Further, TFL2 binds to a subset of Aux/IAA proteins to repress auxin regulated genes involved in ovule and carpel development. In a similar way, TFL2 is also involved in repressing two jasmonate responsive genes, VEGETATIVE STORAGE PROTEIN1 and 2. This TFL2 regulated repression might occur through the interaction with the jasmonate responsive protein JAZ6.

In light signaling TFL2 is involved in repressing both phytochrome A and B signaling as the response to red and far red light is enhanced in tfl2 mutants. The shade avoidance response and chloroplast biogenesis are also regulated by TFL2 as the hypocotyls of tfl2 are not able to elongate as wt in shade conditions and greening is delayed upon de-etiolation of tfl2 seedlings.

This work shows that TFL2 has a repressive function in auxin, jasmonate and light signaling and for the first time we show that TFL2 is directly involved in promoting gene expression.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 52 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 837
Keyword [en]
TERMINAL FLOWER2, auxin, jasmonate, epigenetics, photomorphogenesis
National Category
Botany
Research subject
Biology with specialization in Physiological Botany
Identifiers
URN: urn:nbn:se:uu:diva-151808ISBN: 978-91-554-8099-8OAI: oai:DiVA.org:uu-151808DiVA: diva2:412650
Public defence
2011-06-13, Lindhalssalen, EBC, Norbyvägen 18b, 75236, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-05-23 Created: 2011-04-18 Last updated: 2011-07-01Bibliographically approved
List of papers
1. TFL2/LHP1 is involved in auxin biosynthesis through positive regulation of YUCCA genes
Open this publication in new window or tab >>TFL2/LHP1 is involved in auxin biosynthesis through positive regulation of YUCCA genes
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2011 (English)In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 65, no 6, 897-906 p.Article in journal (Refereed) Published
Abstract [en]

TERMINAL FLOWER2 (TFL2) is the plant homologue of metazoan HETEROCHROMATIN PROTEIN1 (HP1) protein family. It is known that, unlike most HP1 proteins, TFL2 does not primarily localize to heterochromatin; instead it functions in regulation of specific genes in euchromatic regions. We show that the tfl2 mutant has a lower rate of auxin biosynthesis, resulting in low levels of auxin. In line with this, tfl2 mutants have lower levels of expression of auxin response genes and retain an auxin response. The reduced rate of auxin biosynthesis in tfl2 is correlated to the down-regulation of specific genes in the tryptophan-dependent auxin biosynthesis pathway, a sub-set of the YUCCA genes. In vivo, TFL2 is targeted to a number of the YUCCA genes in an auxin-dependent fashion revealing a role of TFL2 in auxin regulation, probably as a component of protein complexes affecting transcriptional control.

Keyword
TERMINAL FLOWER2/LIKE HETEROCHROMATIN PROTEIN1, Aux/IAA, auxin response, auxin biosynthesis, YUCCA, epigenetic
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-150719 (URN)10.1111/j.1365-313X.2010.04470.x (DOI)000288449700005 ()21251106 (PubMedID)
Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2011-07-01Bibliographically approved
2. TERMINAL FLOWER2 is involved in auxin signaling and acts together with IAA6 to repress SHATTERPROOF1 outside its functional domains.
Open this publication in new window or tab >>TERMINAL FLOWER2 is involved in auxin signaling and acts together with IAA6 to repress SHATTERPROOF1 outside its functional domains.
(English)Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-151805 (URN)
Available from: 2011-04-18 Created: 2011-04-18 Last updated: 2011-07-01
3. TERMINAL FLOWER2, an epigenetic repressor involved jasmonate signaling.
Open this publication in new window or tab >>TERMINAL FLOWER2, an epigenetic repressor involved jasmonate signaling.
(English)Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-151806 (URN)
Available from: 2011-04-18 Created: 2011-04-18 Last updated: 2011-07-01
4. Arabidopsis thaliana TERMINAL FLOWER2 is involved in light controlled signaling during seedling photomorphogenesis
Open this publication in new window or tab >>Arabidopsis thaliana TERMINAL FLOWER2 is involved in light controlled signaling during seedling photomorphogenesis
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2012 (English)In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 35, no 6, 1013-1025 p.Article in journal (Refereed) Published
Abstract [en]

Plants respond to changes in the environment by altering their growth pattern. Light is one of the most important environmental cues and affects plants throughout the life cycle. It is perceived by photoreceptors such as phytochromes that absorb light of red and far-red wavelengths and control, for example, seedling de-etiolation, chlorophyll biosynthesis and shade avoidance response. We report that the terminal flower2 (tfl2) mutant, carrying a mutation in the Arabidopsis thaliana HETEROCHROMATIN PROTEIN1 homolog, functions in negative regulation of phytochrome dependent light signalling. tfl2 shows defects in both hypocotyl elongation and shade avoidance response. Double mutant analysis indicates that mutants of the red/far-red light absorbing phytochrome family of plant photoreceptors, phyA and phyB, are epistatic to tfl2 in far-red and red light, respectively. An overlap between genes regulated by light and by auxin has earlier been reported and, in tfl2 plants light-dependent auxin-regulated genes are misexpressed. Further, we show that TFL2 binds to IAA5 and IAA19 suggesting that TFL2 might be involved in regulation of phytochrome-mediated light responses through auxin action.

Keyword
auxin, LIKE HETEROCHROMATIN PROTEIN1, phytochrome, shade avoidance response
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-151807 (URN)10.1111/j.1365-3040.2011.02468.x (DOI)000303052500001 ()
Note

Valdés Ana Elisa and Rizzardi Kristina have contributed equally to this work

Available from: 2011-04-18 Created: 2011-04-18 Last updated: 2013-12-18Bibliographically approved

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