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

The biochemical properties of the ferredoxin/thioredoxin transduction pathw ay regulating the activity of key carbon-fixation enzymes through post-tran slational modifications are well characterized but little is known about th e 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 it, the function of which is still largely u nknown. The effects of light, the circadian clock and active cell division were investigated by northern blotting. The five genes were found to be reg ulated by light and the circadian clock but with different kinetics and amp litudes. This leads for the first time to the proposal that an extra-chloro plastic thioredoxin is possibly implicated in light and/or circadian-relate d processes. An interplay between several light-transduction pathways in co ntrolling the expression of the genes is suggested by the expression studie s and the theoretical analysis of the promoters.