Study On The Molecular Mechanism Of Circadian Clock Regulating The Response Of Arabidopsis Auxin

Plants form a 24-hour rhythm through sensing the cyclical changes in the environment,such as light and temperature.The circadian clock,as a timekeeper,regulates various aspects of plant growth and development.In Arabidopsis thaliana,about one-third of the transcriptome is controlled by clock,which helps plants adapt to the environment.The circadian clock also regulates a variety of signaling pathways,which are activated at different points in 24-hour.As a plant hormone,auxin is necessary for the growth and development.The biosynthesis and precise regulation of auxin signal transduction are the key to the adaptation to environmental changes.The activity of auxin is higher during the day and lower at night.Studies have shown that the circadian clock regulates the induction amplitude of auxin response genes at different times.We know that the circadian clock gates the activity of plant hormone auxin.The circadian clock can also promote auxin production during the day through the transcription factor RVE1,making auxin content higher during the day than at night.Therefore,the circadian clock regulates the diurnal difference of auxin content in plants.To explore how circadian clock regulates auxin response.Firstly,we revisited the auxin responses at different time points.This result indicated that plant response to auxin peaked in dawn and then gradually declined during the daytime.Another feature of auxin is to stimulate hypocotyl elongation.Results showed that the promotion effect of Aux/IAA declined rapidly in the mid-day and reached trough in dusk.CCA1 and LHY are two major oscillators acting in the morning phase in plant circadian clock system.Plants loss of CCA1/LHY(cca1 lhy)showed decreased auxin-responsive gene expression levels and abnormal rhythmicity.Therefore,CCA1/LHY might be a positive regulator for inducing auxin-induced gene expressions.To explore how does CCA1 control auxin sensitivities,we found the interaction between CCA1/LHY with Aux/IAA proteins.We also showed that the domain I and domain II in Aux/IAA proteins interacted with CCA1.Our results showed that CCA1 did not directly affect the IAA17-ARF7 interactions in vitro.We also found that the level of IAA17 protein was negatively correlated with the level of auxin.In summary,this study demonstrated that circadian clock regulates auxin responsive gene expressions through the interaction between CCA1 and IAA17.Therefore,circadian clock gates auxin response at different time points.