Principles of redox control in photosynthesis gene expression

Light is one of the most important environmental factors influencing gene e xpression in photosynthetic organisms. In particular, genes for components of the photosynthetic machinery show light-dependent expression, In recent years, it has become clear that photosynthesis itself contributes important signals to this light control of gene expression by means of changes in th e reduction/oxidation (redox) state of signalling molecules. Such changes i n redox state are induced hy changes in quality and quantity of the inciden t light. Redox signalling mechanisms therefore provide photosynthesis with the possibility of acclimational changes in the structure of the photosynth etic apparatus via a feedback control of photosynthesis gene expression, Th e great variety of these signalling mechanisms is summarised under the term 'redox control'. In some cases, oxygen acts as a different environmental, light-independent stimulus of photosynthetic gene expression, providing an additional redox signal and a different kind of redox control. In this revi ew, we summarise present knowledge about such redox control mechanisms and analyse common properties as well as differences in the various signalling pathways. We suggest that there is an urgent need for a clear distinction b etween different hinds of redox control. Accordingly, we propose a categori sation into perceptional and transductional redox control. These categories are defined and examples given. The generalisation and comparability of re sults obtained in different physiological test systems and species are crit ically discussed.