Daily rhythmic leaf movements and expression of circadian clock genes are differentially synchronized by light in Phaseolus vulgaris

Abstract

Efforts of recent years have achieved significant progress towards the elucidation of the molecular mechanisms underlying the plant circadian clock function. Daily rhythmic leaf movements of leguminous plants belong to the physiological processes controlled by the clock. However, their function and the way they are synchronized by light constitute a controversial subject of plant physiology. Thus, the aim of our study is to explore the role of circadian clock genes in the synchronization of the daily rhythmic leaf movements of the leguminous plant Phaseolus vulgaris. By applying a prototype experimental approach that differentiates the effect of light according to the circadian time, we were able to show that the synchronization of rhythmic leaf movements and of expression of the clock genes PvLHY and PvTOC1 proceeds according to different patterns. By our detailed gene expression analysis we demonstrate that these genes are strongly coupled regarding their adaption to the new phase which suggests that they are interlocked elements of the bean oscillator. Under the same conditions, the leaves' synchronization evolved independently from that of the genes mimicking a rhythm not related to the imposed photoperiod. This novel finding reveals for the first time that the crosstalk between rhythmic transcription and leaf movements is not direct. Our observations establish that the control of the endogenous clock underlying bean leaf movements is exerted on at a level beyond transcription, suggesting many new directions for study.