BREAKTHROUGH REPORT - Large scale measurement of protein synthesis rates over the diurnal cycle reveal pathway specific regulation of translation

Abstract

Plants have a diurnal separation of metabolic fluxes and a need for differential maintenance of protein machinery. To directly assess aggregate protein translation and degradation for specific proteins and to estimate the ATP investment involved, the individual rates of synthesis and degradation of hundreds of different proteins were measured in Arabidopsis thaliana rosettes. Proteins involved in photosynthesis, especially components of the light harvesting complexes, were synthesized much faster in the day (~10:1), while the protein components of carbon metabolism and vesicle tra?icking were translated at similar rates day or night. Comparison of aggregate translation with a range of comparable studies using polysomal or total transcript abundance suggests strong translational control in the diurnal cycle. Diurnal protein degradation rate was observed to be tightly coordinated with protein synthesis rate as few leaf proteins changed in abundance despite reduced translation rates during the night. The direct, quantitative and aggregate analysis of protein synthesis provides an integration of transcriptional, post-transcriptional and translational control of leaf proteome homeostasis and an opportunity to assess the ATP investments involved. The data reveals how the pausing of photosystem synthesis and degradation at night allows the redirection of a decreased energy budget to a selective night-time maintenance schedule.