Circadian control of chloroplast transcription by a nuclear-encoded timing signal.

Circadian timekeeping in plants increases photosynthesis and productivity. There are circadian oscillations in the abundance of many chloroplast-encoded transcripts, but it is not known how the circadian clock regulates chloroplast transcription or the photosynthetic apparatus. We show that, in Arabidopsis, nuclear-encoded SIGMA FACTOR5 (SIG5) controls circadian rhythms of transcription of several chloroplast genes, revealing one pathway by which the nuclear-encoded circadian oscillator controls rhythms of chloroplast gene expression.