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Assessing chemical energy use by plants through new evaluations of costly processes in cellular maintenance

Prof. Harvey Millar, Director of the Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, The University of Western Australia, Perth, Australia

03.05.2018 10:30 Uhr
03.05.2018 11:30 Uhr
Forschungszentrum Jülich, IBG-2, building 06.2, room 406, 2nd floor


A. Harvey Millar
ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Australia

Plants undertake photosynthesis to assimilate CO2 and increase their size, but the efficiency of conversion of fixed photosynthate to growing biomass depends on the costs of growth and the release of fixed carbon through respiration and root exudation. In many plant species over 70% of daily fixed carbon is lost by one of these mechanisms. A key component of the respiratory cost is protein turnover to ensure a functional and dynamic set of proteins optimised for particular developmental stages of plants and their acclimation to the environment. Proteome studies today focus almost exclusively on measuring abundance of proteins and documenting the fact that abundance changes in specific circumstances. Protein abundance data are then sandwiched in systems biology models as a layer between transcript responses and metabolite levels. Instead, analysing protein synthesis and degradation rates provides a new window into the control of protein abundance and the energy expended in maintaining the steady-state proteome across genotypes, development and environments1. They provide the first and second derivative of protein abundance with respect to time: how fast are proteins turning over to achieve steady-state or gaining or lowering abundances and do these speeds change in response to development or the environment? This information can also enable the relative age distribution of a protein population to be assessed. This has implications for the energetic effort employed by the cell to build or maintain a particular activity and gives clues to the impact of age on function in different protein types. We have been using progressive 15N and 13C labelling of plants to provide a birds-eye view of the activity of the proteolysis network as it maintains and sculpts the plant proteome2. Using peptide mass spectrometry, the progressive labelling of new peptides and the decrease in the abundance of peptides with natural isotope profiles enabled the degradation rate of specific proteins to be quantified. This allows deep insights in selective proteolysis of proteins in vivo in different mutant backgrounds. It also enables analysis of the selective degradation of subunits of protein complexes, giving information on the regulation and maintenance of these structures. We have found new rapidly degrading subunits in a variety of protein complexes, identified the set of plant proteins whose degradation rate correlated positively or negatively with leaf growth rate, calculated the protein turnover energy costs for different leaves and their key determinants within the proteome, and are beginning to interpret transcriptome analyses from the point-of-view of the maintenance of the proteome.

1. Nelson CJ, Millar AH (2015) Protein turnover in plant biology. Nature Plants. 1:15017 (doi: 10.1038/nplants.2015.17)
2. Li L, Nelson CJ, Trösch J, Castleden I, Huang S, Millar AH (2017) Protein Degradation Rate in Arabidopsis thaliana Leaf Growth and Development. Plant Cell. 29:207-228 (doi: 10.1105/tpc.16.00768)