Coordination of photosynthetic activity with sunlight benefits plant productivity. Noordally et al. analyzed how the Arabidopsis circadian clock keeps the chloroplasts working in tune with the Sun. SIGMA FACTOR5 (SIG5) is encoded in the cell nucleus and reflects circadian cycles with changes in its own transcript abundance. SIG5 acts, however, in the chloroplast, where it supports photosystem II production.
Z. B. Noordally, K. Ishii, K. A. Atkins, S. J. Wetherill, J. Kusakina, E. J. Walton, M. Kato, M. Azuma, K. Tanaka, M. Hanaoka, A. N. Dodd, Circadian control of chloroplast transcription by a nuclear-encoded timing signal. Science 339, 1316–1319 (2013). [Abstract] [Full Text]