Regulation of chalcone synthase gene expression in wild-type and mutant Arabidopsis

Wade, Helena Kate (1999) Regulation of chalcone synthase gene expression in wild-type and mutant Arabidopsis. PhD thesis, University of Glasgow.

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The regulation of chalcone synthase (CHS) gene expression in Arabidopsis thaliana plants was investigated, icx1 (increased chalcone synthase expression, Jackson et al.,1995, Plant J. 8; 369-380), a mutant altered in the light regulation of CHS expression, was studied in detail. Mature icx1 leaf tissue was found to have increased CHS expression compared to that of wild type plants in UV- A/blue, UV-A and UV-B light. Dark grown icx1 seedlings displayed an increase in CHS expression in the above light qualities and also in far red light. These results indicate that ICX1 acts as a negative regulator downstream of phytochrome, cryptochrome and UV-B photoreceptors and in both mature leaves and seedlings. The synergistic effect of UV-B plus blue light or UV-B plus UV-A light on CHS expression is not altered in the icx1 mutant. A model is presented to explain the position of ICX1 in relation to the inductive and synergistic pathways. Genetic analysis shows that hy5 is epistatic to icx1 and it is proposed that the HY5 transcription factor functions downstream of ICX1 in the light signalling pathway. In addition, the cold induction of CHS is increased in icx1. Therefore ICX1 also regulates a non-light signalling pathway, icx1 has increased expression of other genes involved in flavonoid biosynthesis, encoding dihydroflavonol reductase and chalcone isomerase. The ICX1 gene product does not affect the light regulation of CAB and rbcS genes which are expressed in mesophyll cells. It is proposed that ICX1 acts principally in the epidermis. The induction of CHS expression by UV light was found to be regulated by phytochrome. When mutant plants lacking phytochrome B or both phytochrome B and phytochrome A, were exposed to UV-A light, the resultant CHS expression was lower than that seen in the wild type plants. A red light exposure given to wild type plants prior to UV-A illumination resulted in an increase in CHS expression. In the phyA phyB double mutant the overall induction of CHS was reduced but the increase in CHS expression in red pretreated plants was retained. This increase is most likely regulated by something other than phytochrome A or B. In UV-B light the opposite effect was seen, with an increase in CHS expression in the absence of phytochrome B and in the absence of both phytochromes A and B. The basis for a mutant screen to isolate positive regulators of CHS expression is presented. Transgenic plants containing a cytosine deaminase gene fused to a CHS promoter were produced. These can now be screened for mutants with low CHS expression in response to particular stimuli.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Genetics
Subjects: Q Science > QH Natural history > QH426 Genetics
Colleges/Schools: College of Medical Veterinary and Life Sciences
Supervisor's Name: Jenkins, Dr. Gareth
Date of Award: 1999
Depositing User: Enlighten Team
Unique ID: glathesis:1999-71585
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 May 2019 14:12
Last Modified: 25 Oct 2022 16:23
Thesis DOI: 10.5525/gla.thesis.71585

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