Circadian expression of the light-harvesting complex protein genes in plants

Photosynthesis is one of the important processes that enable Life on earth. To optimize photosynthesis reactions during a solar day, most of them are timed to be active during the light phase. This includes the components of the thylakoid membranes in chloroplasts. Prominent representatives are the proteins of the light-harvesting complex (LHC). The synthesis of both the L hc mRNA and the LHC protein occurs during the day and is regulated by the c ircadian clock, exhibiting the following pattern: increasing levels after s unrise, reaching a maximum around noon, and decreasing levels in the aftern oon. To elucidate the involved control elements and regulatory circuits, th e following strategies were applied: (1) analysis of promoters of Lhc genes , (2) analysis of DNA binding proteins, and (3) screening and investigation of mutants. The most promising elements found so far that may be involved in mediating the circadian rhythmicity of Lhc mRNA oscillations are a myb l ike transcription factor CCA1 (Wang et al. 1997) and the corresponding DNA binding sequence (Piechulla et al. 1998).