Circadian rhy
thms are ubiqui
tous on ear
th from cyanobac
teria
to land plan
ts and animals. Circadian clocks are synchronized
to
the day/nigh
t cycle by environmen
tal fac
tors such as ligh
t and
tempera
ture. In eukaryo
tes, clocks rely on complex gene regula
tory ne
tworks involving
transcrip
tional regula
tion bu
t also pos
t-
transcrip
tional and pos
t-
transla
tional regula
tions. In mul
ticellular organisms clocks are found a
t mul
tiple levels from cells
to organs and whole organisms, making
the s
tudy of clock mechanisms more complex. In recen
t years
the
picoalga
Ostreococcus has emerged as a new circadian model organism
thanks
to i
ts reduced gene redundancy and i
ts minimalis
t cellular organiza
tion. A simplified version of
the “green” plan
t clock, involving
the mas
ter clock genes
TOC1 and
CCA1, has been revealed when
the func
tional genomics and ma
thema
tical model approaches were combined.
Specific photoreceptors such as a blue light sensing LOV histidine kinase mediate light input to the Ostreococcus clock. Non-transcriptional redox rhythms have also been identified recently in Ostreococcus and human red blood cells. This review highlights the progress made recently in the understanding of circadian clock architecture and function in Ostreococcus in the context of the marine environment.
