Shizue Matsubara - Long-term acclimation of Arabidopsis to highly fluctuating light environment

Natural light environment is highly variable in both intensity and spectral quality. The light intensity can vary between zero (night) and >2000 μmol photons m^-2 s^-1 (full sunlight) as the earth rotates, weather changes and wind moves branches and leaves. Upon sudden and large increase in light intensity, photosynthesis is limited biochemically, e.g. by the activation state of RubisCO and the availability of the Calvin-Benson cycle intermediates or inorganic phosphate for ATP synthesis. Low stomatal conductance may also limit plant’s capacity to utilize additional light energy for photosynthesis. When put under highly fluctuating light conditions for days, Arabidopsis plants primarily or initially downregulate photosynthetic light harvesting and linear electron transport while upregulating photoprotection at the expense of carbon gain and growth. Towards understanding the mechanisms of long-term acclimation to highly fluctuating light environment, we studied leaf transcriptome, metabolome and proteome of Arabidopsis (Columbia wild type). Plants were exposed to highly fluctuating light or constant light condition for 3 or 7 days to focus on long-lasting (non-transient) acclimatory changes and downstream responses that may give rise to the phenotypic alterations. Given the pronounced diurnal and circadian variations in leaf metabolism and gene expression, samples were taken at two contrasting time points during the light period in the 12 h/12 h light/dark cycle, namely, early morning and at the end of the day. Furthermore, young and mature leaves were analyzed separately as they typically differ in the photosynthetic capacity. Overall, our results underscore photo-oxidative stress responses and mitigation of acceptor-side limitation to photosynthesis during acclimation to highly fluctuating light. The gene expression profiles revealed distinct responses of young and mature leaves in the morning and at the end of the day, indicating crosstalk between long-term acclimation, leaf development and circadian clock. In particular, I will highlight the changes related to the components of photosynthesis and photoprotection.