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Getting to the root of the issue : characterising plant-microbial circadian interactions in the rhizosphere microbiome
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Newman, Amy Laura (2020) Getting to the root of the issue : characterising plant-microbial circadian interactions in the rhizosphere microbiome. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3520419~S15
Abstract
The circadian clock is an intracellular mechanism that allows organisms to synchronise their internal biological processes with predictable daily environmental changes. The circadian rhythms it generates are well studied in plants. However, very little is known about the possible influence of the plant circadian clock upon root-associated microbiota. Plants form intimate associations with microbes which are recruited from the soil into roots and the soil immediately adjacent to roots. These microbes constitute the rhizosphere microbiome and its composition can have significant implications for plant health. This thesis therefore investigated the presence of circadian changes in the rhizosphere microbiome and demonstrated the role of the plant circadian clock in shaping these interactions. To investigate the influence of the plant circadian clock on the assembly of the rhizosphere microbiome, we compared the rhizosphere bacterial and fungal communities of wild-type plants with those of plants with abnormal circadian clocks, using amplicon sequencing of the 16S rRNA and ITS regions. We found that altered clock function through overexpression or loss-of-function of the core plant clock gene lhy (late elongated hypocotyl) altered the rhizosphere microbiome after a period of plant growth, indicating that the plant circadian clock influences rhizosphere microbiome assembly. Additionally, we showed that a fraction of microbial OTUs exhibit daily changes in activity or abundance. OTUs that showed rhythmicity were found to
differ between wild-type and lhy mutant plants, indicating that the plant clock also
influences diel changes in the rhizosphere microbiome. In order to determine whether microbial rhythmicity in the rhizosphere persists in the absence of daynight
cycles, we subsequently characterised microbial communities from plants transferred to constant light and temperature conditions. Here, rhythmic OTUs were observed in the wild-type rhizosphere but rhythmicity was largely abolished in the rhizosphere of arrhythmic plants overexpressing lhy, indicating that most free-running microbial rhythmicity was driven by the plant circadian clock. A handful of rhythmic OTUs were found in samples from arrhythmic plants, providing evidence for autonomous rhythmicity in some rhizosphere microbiota. Further, we developed a flexible imaging method for the non-destructive visualisation of temporal interactions between plant roots and a luminescent model rhizosphere bacterium. Rhythmic bacterial luminescence was observed under light-dark cycles and persisted on the roots of wild-type plants under constant conditions. This free-running rhythmicity was disrupted on plants with loss-of-function of the circadian clock gene gi (gigantea), indicating that it was driven by the plant circadian clock. In summary, the work presented in this thesis identified circadian changes in the rhizosphere microbiome and found that the plant circadian clock drives most of these oscillations. The rhizosphere microbiome is therefore more variable over very short timescales than previously anticipated. The time of day at which samples are taken should be considered in future studies seeking to investigate rhizosphere microbiota, as this factor is not currently controlled for. Additionally, the findings of this thesis may form the basis of new strategies for more sustainable agricultural production, such as the timed application of crop management products.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QK Botany Q Science > QR Microbiology S Agriculture > SB Plant culture |
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Library of Congress Subject Headings (LCSH): | Plant-microbe relationships, Plant circadian rhythms, Rhizosphere, Plant health | ||||
Official Date: | November 2020 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | School of Life Sciences | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Bending, Gary ; Carré, Isabelle | ||||
Sponsors: | Natural Environment Research Council (Great Britain) | ||||
Extent: | xvi, 191 leaves : illustrations, charts | ||||
Language: | eng |
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