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Effects of a genetically modified potato line with altered starch metabolism on carbon fluxes within the plant-soil system and on microbial community structure and function in the rhizosphere [Elektronische Ressource] / Silvia Gschwendtner

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TECHNISCHE UNIVERSITÄT MÜNCHEN Lehrstuhl für Bodenökologie Effects of a genetically modified potato line with altered starch metabolism on carbon fluxes within the plant-soil system and on microbial community structure and function in the rhizosphere Silvia Gschwendtner Vollständiger Abdruck der von der Fakultät Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt der Technischen Universität München zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften genehmigten Dissertation. Vorsitzende(r): Univ.-Prof. Dr. J.C. Munch Prüfer der Dissertation: 1. Hon.-Prof. Dr. M. Schloter 2. Univ.-Prof. Dr. R. Hückelhoven Die Dissertation wurde am 05.08.2010 bei der Technischen Universität München eingereicht und durch die Fakultät Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt am 12.10.2010 angenommen. List of Publications and contributions Publications . Gschwendtner S, Reichmann M, Müller M, Radl V, Munch JC, Schloter, M. 2010. Abundance of bacterial genes encoding for proteases and chitinases in the rhizosphere of three different potato cultivars. Biology and Fertility of Soils 46(6): 649-652 . Gschwendtner S, Reichmann M, Müller M, Radl V, Munch JC, Schloter M. 2010.

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Published 01 January 2010
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TECHNISCHE UNIVERSITÄT MÜNCHEN

Lehrstuhl für Bodenökologie


Effects of a genetically modified potato line with altered starch metabolism on
carbon fluxes within the plant-soil system and on microbial community
structure and function in the rhizosphere

Silvia Gschwendtner

Vollständiger Abdruck der von der Fakultät Wissenschaftszentrum Weihenstephan für Ernährung,
Landnutzung und Umwelt der Technischen Universität München zur Erlangung des akademischen
Grades eines
Doktors der Naturwissenschaften
genehmigten Dissertation.



Vorsitzende(r): Univ.-Prof. Dr. J.C. Munch

Prüfer der Dissertation: 1. Hon.-Prof. Dr. M. Schloter
2. Univ.-Prof. Dr. R. Hückelhoven


Die Dissertation wurde am 05.08.2010 bei der Technischen Universität München eingereicht und
durch die Fakultät Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt
am 12.10.2010 angenommen.
































List of Publications and contributions

Publications

. Gschwendtner S, Reichmann M, Müller M, Radl V, Munch JC, Schloter, M. 2010. Abundance
of bacterial genes encoding for proteases and chitinases in the rhizosphere of three different
potato cultivars. Biology and Fertility of Soils 46(6): 649-652

. Gschwendtner S, Reichmann M, Müller M, Radl V, Munch JC, Schloter M. 2010. Effects of
genetically modified amylopectin-accumulating potato plants on the abundance of beneficial and
pathogenic microorganisms in the rhizosphere. Plant and Soil 335(1): 413-422

 . Gschwendtner S, Esperschütz J, Buegger F, Reichmann M, Müller M, Munch JC, Schloter M.
Effects of a genetically modified starch metabolism in potato plants on photosynthate fluxes into
the rhizosphere and on microbial degraders of root exudates. FEMS Microbiology Ecology,
submitted


My contribution to the publications

   I took part in planning the experiments, performed the samplings and conducted the
subsequent laboratory analyses. In addition, all statistical evaluation of the results was done
by myself. The manuscripts are based mainly on my input.

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Wollte man warten, bis man etwas so gut könnte,
dass niemand etwas daran auszusetzen fände,
brächte man nie etwas zuwege...
(Friedrich Nietzsche)
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Table of Contents

Summary 1
Zusammenfassung 3
1. Introduction to the Ph.D. thesis 5
2. Genetically modified plants 6
3. Legislation regarding genetically modified plants in the European Union 8
4. Monitoring process for genetically modified plants 9
5. Genetically modified potatoes with altered starch quality 10
5.1. Industrial applications of starch 10
5.2. The two starch components: Amylose and amylopectin 11
5.3. The amylopectin-accumulating potato 12
6. The rhizosphere 13
6.1. General definition 13
6.2. Plant-microbe interactions 15
6.2.1. Harmful interactions 15
6.2.2. Beneficial interactions 18
6.2.3. Neutral interactions 20
7. Molecular tools to study microbial communities in soil ecosystems 21
7.1. Quantitative real-time PCR 23
7.2. Phospholipid fatty acid analysis 26
7.3. Stable isotope probing 28
8. Outline of the Ph.D. thesis 29
9. General and summarizing discussion 32
9.1. Effects of genetic modification on the abundance of microorganisms with
specific ecological function in the rhizosphere 33
9.2. Effects of genetic modification on carbon partitioning within plant and
rhizosphere microbial community 35
9.3. Greenhouse versus field studies 36
10. Conclusions 38
References 39
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List of abbreviations 55
Acknowledgements 57
Publication  60
Publication  66
Publication   78

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Summary

Despite the many benefits offered by genetically modified (GM) plants, their commercialization is still
highly controversially discussed in many countries, raising questions about potential adverse effects
on human and environmental health. Among the major concerns are the possibility of creating invasive
plant species, the unintended consequences of transgene flow to indigenous plants and
microorganisms, development of super pests, and the effects of transgenic plants on non-target
organisms. Although the importance of soil microbes for ecosystem functioning and plant performance
is well acknowledged, the impact of GM plant cultivation on belowground biomass has long been
neglected in risk assessment. As plants contribute substantially to soil carbon content via root
exudation, they are hypothezised to govern the development of beneficial microbial communities in
their rhizosphere, which in turn promote plant growth and health by various mechanisms like nutrient
mobilization, production of plant growth hormones, induction of systemic resistance in the host plant
and/or by acting as biocontrol agents. Therefore, it has to be evaluated if genetic engineering affects
carbon fluxes from plant into soil and thus microbial community structure.
Hence, to assess potential impacts of the growth of amylopectin-accumulating GM potato line #1332
(Solanum tuberosum L., Bayerische Landesanstalt für Landwirtschaft (LfL)) on associated soil
microorganisms, two greenhouse experiments and a 1-year-1-site field study included in a great scale
release of the respective GM potato line were conducted in a randomized experimental design.
Besides the parental variety ‘Walli’, a second non-transgenic potato cultivar was planted, in order to
relate possible GM-dependent effects to natural variation among different plant genotypes.
Rhizosphere samples were taken at young leaf developmental and at flowering stage of potatoes. For
investigation of carbon fluxes within the plant-rhizosphere system and microbial community structure,
13C stable isotope probing (SIP) in combination with phospholipid fatty acid (PLFA) analysis was
chosen. To get a more detailed insight into rhizosphere microbial populations, abundance pattern of
important potato pathogens (Clavibacter michiganensis, Phytophthora infestans), plant beneficial
microbes (Pseudomonas spp., Trichoderma spp.), and functional groups involved in soil mineralization
processes were examined using quantitative real-time PCR (qPCR). Additionally, total bacterial and
fungal abundance pattern (based on 16S rRNA, ITS rRNA) were determined.
The genetic modification present in potato line #1332 had no influence on carbon partitioning within
the plant, on plant derived carbon within the pool of water extractable organic carbon (WEOC) in the
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rhizosphere, or on rhizosphere community structure and activity. Furthermore, no differences in
abundance pattern of phylogenetic groups and functional genes under investigation between the GM
line and its parental variety ‘Walli’ were observed. Nevertheless, the non-transgenic potato cultivars
varied significantly regarding to carbon partitioning from plant into soil, rhizosphere population
structure and microbial gene abundance pattern. Moreover, also plant developmental stage affected
carbon fluxes via plant into rhizosphere and, subsequently, microbial community structure and gene
abundance.
When comparing data obtained from greenhouse and field, the impact of cultivar and plant vegetation
stage on microbial populations was much more pronounced in the latter. Furthermore, the rhizosphere
of field-grown potatoes showed a significantly higher abundance of microorganisms than that of plants
grown under greenhouse conditions.

Altogether, genetic modification of potato line #1332 seemed not to influence carbon partitioning
through plant into soil or microbial community structure and abundance in the rhizosphere. However, it
has to be considered that a generalization in respect of risk assessment and monitoring is not
possible, as data were obtained in greenhouse studies under optimal growth conditions and a 1-year-
1-site field trial. Therefore, for evaluation of long-term effects further field studies lasting several years
and including different sites have to be conducted.
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