The complex regulation of ferredoxin/thioredoxin-related genes by light and the circadian clock

The biochemical properties of the ferredoxin/thioredoxin transduction pathway regulating the activity of key carbon-fixation enzymes through post-translational modifications are well characterized but little is known about the regulation of the different genes. In the present study, we investigated in Chlamydomonas reinhardtii the regulation of the expression of ferredoxin, thioredoxin m, ferredoxin-NADP reductase, phosphoribulokinase, as well as that of cytosolic thioredoxin h, the function of which is still largely unknown. The effects of light, the circadian clock and active cell division were investigated by northern blotting. The five genes were found to be regulated by light and the circadian clock but with different kinetics and amplitudes. This leads for the first time to the proposal that an extra-chloroplastic thioredoxin is possibly implicated in light and/or circadian-related processes. An interplay between several light-transduction pathways in controlling the expression of the genes is suggested by the expression studies and the theoretical analysis of the promoters.