Hypothesis: A binary redox control mode as universal regulator of photosynthetic light acclimation

Abstract

In nature, plants experience considerable changes in the prevailing illumination, which can drastically reduce photosynthetic efficiency and yield. Such adverse effects are counterbalanced by acclimation responses which ensure high photosynthetic productivity by structural reconfiguration of the photosynthetic apparatus. Those acclimation responses are controlled by reduction-oxidation (redox) signals from two pools of redox compounds, the plastoquinone and the thioredoxin pools. The relative impact of these two redox signaling systems on this process, however, remains controversial. Recently, we showed that photosynthesis controls nuclear gene expression and cellular metabolite states in an integrated manner, thus, stabilizing the varying energetic demands of the plant. Here, we propose a novel model based on a binary redox control mode to explain adaptation of plant primary productivity to the light environment. Plastoquinone and thioredoxin pools are proposed to define specific environmental situations cooperatively and to initiate appropriate acclimation responses controlled by four binary combinations of their redox states. Our model indicates a hierarchical redox regulation network that controls plant primary productivity and supports the notion that photosynthesis is an environmental sensor affecting plant growth and development.

Keywords: arabidopsis; photosynthetic light acclimation; plant fitness; redox control; sensor function.

Figure 1

Working hypothesis of cooperative redox signaling in photosynthetic acclimation. Illumination conditions induce changes in relative redox poises of PQ and Trx pools (black arrows: change towards a more oxidized state, white arrows: change towards a more reduced state). Combinations of them serve as input signals which affect gene expression networks and metabolic enzyme activities in a coordinated and parallel manner. Network interactions then initiate respective output response programmes resulting in defined metabolic states. Indicated redox balances are based on data from this and recent studies.,