Plants respond to environmental signals by following growth responses termed tropisms. like gravity, light and touch. Root gravitropism, for example, is the response by which the primary root orients its growth according to the gravity vector. There is a lot of genetic and molecular evidence that support the crucial role of the phytohormone auxin during root gravitropism. For example mutations in genes' encoding aux in synthesis, signalling and transport proteins resulted in agravitropic or partially agravitropic phenotypes. Two novel auxin biosensors, DII-VENUS and DR5:VENUS had been used to monitor auxin abundance and auxin response respectively in mutants affecting the above mentioned aux in processes, Results reflected the powers of these 2 reporters combined as they \,,,'ere able to reflect a tight relation between the root tip bending and the formation of an auxin gradient following a 90° gravistimulus, They were also able to uncover unexpected effects on auxin homeostasis in arj7arf19 that were validated by gas chromatography- based studies. Despite the wealth of information describing a lot of auxin mutants, there are a lot of genes that had not been characterised yet. So, a transcriptomics approach was followed to discover some of these genes, Results showed thai over 500 genes were observed to be differentially expressed following a gravity stimulus over an 8 hours time course. Many of these genes were shown to be expressed in an ARF7/ARFI9 dependant manner. Functional studies identified several mutants which had slower rate of bending following a 90° gravistimulus: AT5G47540 (similar to M025 protein; unknown function), AT2G27660 (Del -domain containing protein, zinc ion binding: unknown function) and AT2G25900 (ATCTH; Transcription factor containing a CCCH-type zinc ion binding domain). Although a lot of work has been done on root gravitropism in A. Ihaliana, the natural variation within this model system was not explored a lot. So, the Gravitropic Set Angle (GSA) - or the angle at which the root normally grows with respect to the gravity vector - for the Arabidopsis ecotype, from the Cape Verde islands (Cvi) was studied in comparison with the laboratory strain Landsberg erecta (Ler-l). The GSA phenotype in the Cvi ecotype shows a skewing of the primary root to the left at an angle of about 90°, Using Near Isogenic Lines (NILs), this root trait was shown to be controlled by a Cvi-0 region on chromosome 2. This region was mapped to a region between 11. 16 Mb and 11.28 Mb.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:594873 |
| Date | January 2013 |
| Creators | Hijazi, Hussein |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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