Abstract

Circadian timekeeping improves plant performance. Understanding the cellular basis for the circadian optimization of plant function is important, because this could unlock additional agricultural productivity. There are circadian rhythms of photosynthesis and correct circadian regulation increases plant productivity, but it is not known how the circadian oscillator regulates the photosynthetic apparatus or the chloroplast genome. I will show that in Arabidopsis, a subset of chloroplast-encoded photosynthesis genes is controlled by a nuclear-encoded signalling protein. Our findings reveal one pathway by which the nuclear-encoded circadian oscillator controls rhythms of chloroplast gene expression. I will show that light and circadian signals are integrated to adjust chloroplast transcription. I will conclude that (i) during evolution, prokaryotic transcriptional regulators in chloroplasts were recruited by the eukaryotic circadian system in higher plants, and (ii) circadian timing information is communicated between organelles with distinct genetic systems.