Nodules and lateral roots are both key organs for the uptake of nutrients by plants. During nodulation, leguminous plants form root nodules, housing symbiotic Rhizobial bacteria able to fix atmospheric nitrogen, allowing the plant to utilise it. Lateral roots are formed by all plants and allow the root system to be extended laterally, increasing the region of soil from which nutrients may be taken up. Formation of lateral roots and nodules share developmental features such as single cell-type origins of the primordia, and hormonal and nutrient regulatory mechanisms, so it is hypothesised that the evolution of nodulation co-opted elements of pre-existing genetic mechanisms of lateral root formation. To test this hypothesis, Arabidopsis thaliana (non-legume) genes similar to known Medicago truncatula (legume) nodulation genes were screened for phenotypic effects. Mutants of Arabidopsis NODGS and a GRAS-domain SCR-like transcription factor were found to confer lateral root phenotypes, suggesting evidence for the co-option hypothesis. The mutants were examined further using cell-type specific transcriptomics through Fluorescence-Activated Cell Sorting (FACS) to identify genomic components underlying the possible co-option. For the purposes of future research, the translation of FACS transcriptomics to Medicago was evaluated, validating microarray probe design for the most recent genome annotation but also highlighting challenges faced in analysing more complex plant roots. The GRAS-domain SCR-like transcription factor mutant was found to modulate lateral root development through pathways involving the phytohormone gibberellic acid (GA). Treatment with GA rescued some components of the GRASdomain SCR-like transcription factor phenotype, indicating a potential role for the gene in activating GA biosynthesis. A second mutant, of NODGS, was also found to affect lateral root development with some dependence on nitrate level. Existing knowledge suggested a role in root morphogenesis and flagellin-triggered signalling, and this work implies a level of cell-type specificity in gene function.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:582482 |
| Date | January 2013 |
| Creators | Carter, Anthony D. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/58037/ |
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