CHLOROPLAST REDOX REGULATION OF NUCLEAR GENE-TRANSCRIPTION DURING PHOTOACCLIMATION

The role of the redox state of ferredoxin/thioredoxin within the chlor oplast is well established for the feedback regulation of enzyme activ ity in the Calvin cycle. However, evidence has emerged also suggesting that chloroplast electron transport components regulate plastid and n uclear gene expression. Using the unicellular green alga, Dunaliella t ertiolecta, as a model organism, we have shown that the cell acclimate s to changes in growth irradiance by altering the abundance and activi ties of photosynthetic components, in particular the light harvesting complexes (LHC). Pharmacological data suggests that light intensity is sensed through the redox status of the plastoquinone pool leading to the regulation of nuclear encoded genes, such as Lhcb. This signal may be transduced through a redox regulated protein kinase that (in)direc tly interacts with the nuclear transcription apparatus. The redox stat e of the plastoquinone pool seems to play a pivotal role in sensing ce llular energy status and in regulating photosynthetic capacity. Other cellular pathways, including carbon fixation, carbohydrate metabolism and nutrient assimilation have been shown to have feedback influences on photosynthesis, that may be sensed by the redox state of the plasto quinone pool.