|dc.contributor.author||Ganpudi, Ashwin Laxminaranyan||
|dc.description.abstract||Light energy serve as primary substrates for photosynthetic sugar production
in plant metabolic maintenance. In addition, light also functions as a crucial
environmental cue initiating a series of signal transduction cascades downstream to
the photoreceptors. Limited knowledge exists on the molecular connections
integrating the metabolic and photoreceptor signalling pathways.
The primary focus of this thesis is the plant glucose receptor Hexokinase1
(HXK1). Arabidopsis HXK1 performs a dual function 1) an enzymatic role in
glycolysis catalysing glucose phosphorylation to generate glucose-6-phosphate (G6P)
and 2) a transcriptional repressor role in response to exogenous sugar. While the
enzymatic role required for ATP production during respiration is conserved across
biological systems, the sugar induced nuclear signalling role has only been identified
in yeast and Arabidopsis.
In this thesis, I show that HXK1 operates during nutrient limiting conditions
such as extended periods of darkness or suboptimal light in seedlings. A first-ever
RNAseq enabled us to gain insights into the mutant transcriptome. Energy demanding
pathways were downregulated and carbon starvation induced Branched Chain Amino
Acid (BCAA) degradation pathway is upregulated as an alternate energy source.
Supplying Glucose-6-Phosphate (G6P – HXK1 enzymatic endproduct) restored the
mutant phenotype and the C starvation response during nutrient limited conditions.
This highlights the requirement of HXK1 enzyme rather than the signalling component
during seedling establishment. Nuclear HXK1 operates as a transcriptional repressor
in response to exogenous sugar. It is postulated to function during feedback inhibition
of photosynthetic genes. However, our data indicates that this does not appear to be
the case when endogenous sugars are naturally elevated in seedlings.
Further, I present preliminary data on the potential feedback regulation by
HXK1Overpression (HXK1OX) in blue and red light signalling pathway. HXK1
exerts a negative control on blue light mediated photomorphogenesis. Red light
negates this effect in a PHYB dependent manner. Although the transcriptomes are
reflective of the phenotype, the molecular mechanism behind this response is unknown.
Taken together, my thesis discovers novel facets of HXK1 during seedling
|dc.publisher||The University of Edinburgh||en
|dc.relation.hasversion||Krahmer J, Ganpudi A, Abbas A, Romanowski A, Halliday KJ (2018) Phytochrome, Carbon Sensing, Metabolism, and Plant Growth Plasticity. Plant Physiol. 176(2):1039-1048||en
|dc.relation.hasversion||Seaton D, Toledo-Ortiz G, Ganpudi A, Kubota A, Imaizumi T, Halliday KJ (2018) Dawn and photoperiod sensing by phytochrome A. Proc. Natl. Acad. Sci. USA. 2018 www.pnas.org/cgi/doi/10.1073/pnas.1803398115||en
|dc.subject||nutrient limiting conditions||en
|dc.title||Role of the Arabidopsis Glucose Sensor Hexokinase1 (HXK1) in seedling establishment||en
|dc.type||Thesis or Dissertation||en
|dc.type.qualificationname||PhD Doctor of Philosophy||en