Increased sucrose levels mediate selective mRNA translation in Arabidopsis

Background: Protein synthesis is a highly energy demanding process and is regulated according to cellular energy
levels. Light and sugar availability affect mRNA translation in plant cells but the specific roles of these factors remain
unclear. In this study, sucrose was applied to Arabidopsis seedlings kept in the light or in the dark, in order to
distinguish sucrose and light effects on transcription and translation. These were studied using microarray analysis
of steady-state mRNA and mRNA bound to translating ribosomes.
Results: Steady-state mRNA levels were affected differently by sucrose in the light and in the dark but general
translation increased to a similar extent in both conditions. For a majority of the transcripts changes of the transcript
levels were followed by changes in polysomal mRNA levels. However, for 243 mRNAs, a change in polysomal occupancy
(defined as polysomal levels related to steady-state levels of the mRNA) was observed after sucrose treatment in the
light, but not in the dark condition. Many of these mRNAs are annotated as encoding ribosomal proteins, supporting
specific translational regulation of this group of transcripts. Unexpectedly, the numbers of ribosomes bound to each
mRNA decreased for mRNAs with increased polysomal occupancy.
Conclusions: Our results suggest that sucrose regulate translation of these 243 mRNAs specifically in the light, through a
novel regulatory mechanism. Our data shows that increased polysomal occupancy is not necessarily leading to
more ribosomes per transcript, suggesting a mechanism of translational induction not solely dependent on
increased translation initiation rates.