Ribosome and transcript copy numbers, polysome occupancy and enzyme dynamics in Arabidopsis

Abstract

Plants are exposed to continual changes in the environment. The daily alternation between light and darkness results in massive recurring changes in the carbon budget, and leads to widespread changes in transcript levels. These diurnal changes are superimposed on slower changes in the environment. Quantitative molecular information about the numbers of ribosomes, of transcripts for 35 enzymes in central metabolism and their loading into polysomes is used to estimate translation rates in Arabidopsis rosettes, and explore the consequences for important sub-processes in plant growth. Translation rates for individual enzyme are compared with their abundance in the rosette to predict which enzymes are subject to rapid turnover every day, and which are synthesized at rates that would allow only slow adjustments to sustained changes of the environment, or resemble those needed to support the observed rate of growth. Global translation rates are used to estimate the energy costs of protein synthesis and relate them to the plant carbon budget, in particular the rates of starch degradation and respiration at night.

Combined Large-Scale Phenotyping and Transcriptomics in Maize Reveals a Robust Growth Regulatory Network

“…Since protein synthesis is one of the most energyconsuming processes in the cell, one can expect selective pressure to achieve a frugal use of the translational machinery (Perry, 2007). Thus, a more efficient translational machinery that minimizes the indirect costs of protein synthesis is likely to allow a higher rate of cell proliferation and growth (Lempiäinen and Shore, 2009;Piques et al, 2009), a possible explanation for the anticorrelation we observe between transcript levels of genes encoding for ribosomal proteins and leaf size and timing traits.…”

Leaf Starch Turnover Occurs in Long Days and in Falling Light at the End of the Day

“…Although transcript levels for many enzymes of starch degradation rise with time after dawn, there is evidence for enzymes including glucan, water dikinase, a-amylase 3 (AMY3), and the glucanotransferase DPE2 that the amount of protein varies very little over the day-night cycle Lu et al, 2005;Yu et al, 2005;Skeffington et al, 2014). In general terms, marked diel fluctuations in amounts of enzymes of primary metabolism are unlikely because of their high abundance and long half-lives (Gibon et al, 2004;Piques et al, 2009;Baerenfaller et al, 2012;Nelson et al, 2014). An intriguing exception is the major starch-degrading enzyme BAM3, which was recently shown to have a very short half-life of only 0.43 d (Li et al, 2017).…”

The Arabidopsis nox Mutant Lacking Carotene Hydroxylase Activity Reveals a Critical Role for Xanthophylls in Photosystem I Biogenesis

“…Polysomes were fractionated from crude leaf extracts as described (Piques et al, 2009) but using 100 to 150 mg fresh weight. The gradients were fractionated using a programmable density gradient fractionation system (Teledyne Isco) to continuously record absorbance at 254 nm.…”