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ABSTRACT
Respiratory oxidative phosphorylation is a cornerstone of cellular metabolism
allowing the development of eukaryotic and ultimately aerobic multi-cellular
organisms. Being the largest of the energy-transducing complexes of the
respiratory chain, Complex I is composed of 44 subunits in Arabidopsis. These
subunits are encoded either by nuclear or mitochondrial genes; remarkably,
over 20% of them are plant-specific.
We characterized an Arabidopsis mutant, ndufs4, lacking complex I, which has
constitutively lowered phosphorylation efficiency. The lack of complex I has
no pleiotropic effects on other respiratory components but promotes broad
changes in the nuclear transcriptome governing growth and photosynthetic
function. We observed large increases in organic acid and amino acid pools in
the mutant, especially at night, concomitant with large increases in the
cellular inorganic phosphate pool s. While germination is delayed this can be
rescued by application of GA, and root growth assays of seedlings show enhanced
tolerance to cold, mild salt and osmotic stress. Our data suggest that the
absence of complex I alters the adenylate control of cellular metabolism and
provide insights into how cellular metabolism flexibly adapts to reduced
phosphorylation efficiency and why this state may benefit the plant by
providing moderate stress tolerance.
My future research will build on this analysis of the effects of altered
phosphorylation efficiency on cellular metabolism and plant growth. A set of
Arabidopsis mutants with different degrees of respiration impairment will
provide a system in which the role of respiration on redox homeostasis,
cellular metabolism and ROS signalling can be studied. I intend to
characterize these mutants in order to understand how a respiratory defect
can influence other metabolic pathways such as glycolysis, photosynthesis or
photorespi ration. I will moreover investigate the assembly of complex I and
its functions, especially a plant-specific role in exporting CO2 produced
during photorespiration.
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