Iron and ammonium sensing differentially modulate root plasticity in Arabidopsis thaliana [Elektronische Ressource] / presented by Joni Esrom Lima

Joni Esrom Lima

Informations

• Publié par: universitat_hohenheim
• Publié le: 01 janvier 2010
• Nombre de lectures: 30
• Langue: English
• Poids de l'ouvrage: 20 Mo

Extrait

Institute of Plant Nutrition
University of Hohenheim
Prof. Dr. Nicolaus von Wirén
Iron and ammonium sensing differentially modulate
root plasticity in Arabidopsis thaliana
Dissertation
Submitted in fulfillment of the requirements for the degree
“Doktor der Agrarwissenschaften”
(Dr. Sc. agr. / Ph.D in Agricultural Sciences)
to the
Faculty of Agricultural Sciences
presented by
Joni Esrom Lima
from Brazil
201023This thesis was accepted as a doctoral dissertation in fulfillment of the requirements
for the degree “Doktor der Agrarwissenschaften” by the Faculty of Agricultural
Sciences at the University of Hohenheim.
thDate of the oral examination: 24 September 2010
Examination Committee
Supervisor and reviewer Prof. Dr. Nicolaus von Wirén
Co-reviewer Prof. Dr. Gerd Weber
Additional examiner Prof. Dr. Andreas Schaller
Dean and head of the committee Prof. Dr. Andreas Fangmeier
45Table of contents
1. Summary- Zusammenfassung 1
1.1. Summary ..........................................................................................................1
1.2. Zusammenfassung ............................................................................................2
2. General introduction 4
2.1. The root system .................................................................................................4
2.1.1. Lateral root development ...............................................................................5
2.2. Root plasticity ..................................................................................................13
2.2.1. Nitrate signaling and nitrate-induced root plasticity ......................................13
2.2.2. Ammonium transport and signaling in yeast and plants ..............................15
2.2.3. Phosphorus-regulated root plasticity ............................................................18
2.2.4. Sulfur-regulated root plasticity ......................................................................19
2.2.5. Potassium-regulated root plasticity ..............................................................20
2.2.6. Iron signaling and iron acquisition ................................................................21
2.3. Objectives of the thesis ...................................................................................25
3. Local Supply of Iron Distinctly Defines Lateral Root Number and Elongation
in Arabidopsis thaliana 26
3.1. Introduction ......................................................................................................26
3.2. Material and methods ......................................................................................28
3.2.1. Plant material and growth conditions ...........................................................28
3.2.2. Root growth measurements .........................................................................28
3.2.3. Histochemical analysis .................................................................................29
3.2.4. Histochemical localization of iron .................................................................29
3.2.5. Expression analysis 30
3.2.6. Mineral element and chlorophyll analysis ....................................................30
3.3. Results ............................................................................................................31
63.3.1. Localized supply of iron stimulates lateral root development in Arabidopsis
.....................................................................................................................31
3.3.2. Influence of the mode of iron supply on the nutritional status of the shoot ..35
3.3.3. Effect of localized Fe supply on early lateral root development ...................39
3.3.4. Involvement of IRT1 in the differential response of the number and length of
lateral roots to localized iron supply .............................................................41
3.3.5. Influence of FIT on lateral root development under localized iron supply ....43
3.3.6. Influence of FRD3 on lateral root development and the expression of Fe-
responsive genes .........................................................................................44
3.4. Discussion .......................................................................................................49
3.4.1. Localized Fe supply differentially regulates lateral root number and lateral
root length ....................................................................................................49
3.4.2. The local regulation of lateral root development by iron ..............................50
4. Ammonium triggers lateral root branching in Arabidopsis in an AMT1;3-
dependent manner 53
4.1. Introduction ......................................................................................................53
4.2. Material and methods ......................................................................................55
4.2.1. Plant Material ...............................................................................................55
4.2.2. Plant in vitro culture 56
4.2.3. Heterologous expression of AMT1;3 mutants in yeast .................................56
4.2.4. Root growth measurements .........................................................................57
4.2.5. Histochemical analysis and microscopy .......................................................57
4.2.6. Gene expression analysis ............................................................................58
4.2.7. Accession Numbers .....................................................................................58
4.3. Results ............................................................................................................59
4.3.1. Lateral root formation is stimulated by local ammonium supply ...................59
4.3.2. Ammonium-induced lateral root branching is subject to systemic repression
.....................................................................................................................64
4.3.3. Ammonium and nitrate regulate lateral root development in a
complementary way .....................................................................................71
4.3.4. The ammonium transporter-defective mutant qko shows decreased
ammonium-triggered lateral root branching .................................................72
4.3.5. The role of AMT1;3 in lateral root branching ................................................74
74.3.6. Ammonium promotes lateral root initiation to local auxin signalling ............84
4.4. Discussion .......................................................................................................88
4.4.1. A complementary role for ammonium and nitrate in lateral root development
.....................................................................................................................88
4.4.2. The possible function of AMT1;3 in ammonium-triggered lateral root
development .................................................................................................90
5. General discussion 93
5.1. Environmental factors and responses in the root system ................................93
5.2. Systemic versus local nutrient signaling-responses controlling root
morphology .................................................................................................103
5.3. The nutrient transceptor model for coordinating changes in root morphology
....................................................................................................................106
6. References 109
7. Acknowledgments 124
8. Curriculum vitae 127
81. Summary- Zusammenfassung
1.1. Summary
Plant growth depends on a continuous nutrient uptake by roots. In natural or
agricultural ecosystems nutrients are often sparingly available and subject to a non-
homogenous or patchy distribution in the rooted soil volume. Plants may then alter
their root system architecture to better exploit nutrient patches in the soil. Directed
root growth towards a nutrient source may be seen as an indication for nutrient
sensing. So far, changes in root system architecture have been systematically
investigated only for nitrate, sulphate and phosphate. It was therefore the aim of this
thesis to investigate changes in root morphology to other nutrients which are
restricted in their mobility in soils, namely iron and ammonium.
The first part of the present thesis describes how the root system architecture is
altered by localized iron (Fe) supply. In the low concentration range, increasing Fe
concentrations in a homogenous or localized supply enhanced lateral root number in
a similar manner. Lateral root length, however, was twofold higher under localized
relative to homogenous Fe supply. With further increasing Fe concentrations lateral
root length was repressed even though shoot growth was unaffected. Using
Arabidopsis mutants which are defective in Fe acquisition or Fe translocation within
the plant, it was possible to show that lateral root elongation is under control of a
local rather than a systemic regulatory loop involving the high-affinity Fe transporter
IRT1.
The second part of the thesis describes and investigates a novel phenotype in root
system architecture that depends on localized ammonium supply. Under these
conditions, Arabidopsi