Diurnal and circadian regulation of salt tolerance in Arabidopsis

Abstract

Most living organisms have a circadian clock, which coordinates their internal biological events with external environmental signals. Recent work showed that the Arabidopsis circadian clock regulates the plant's responses to stresses such as drought, cold, pathogens, and wounding. However, the link between the circadian clock and the plant's response to salinity, which retards plant growth and reduces crop yields, has not yet been investigated. In this study, we showed that tolerance to salinity stress is regulated by the diurnal cycle in Arabidopsis. The salt-induced expression of the salt- and drought-responsive transcription factor gene RD29A depends on the time of day and the transcription of the Na+/H+ antiporter gene SOS1 is under the control of the circadian clock. Furthermore, accumulation of SOS1 protein upon salt stress in transgenic plants that constitutively overexpress SOS1 (SOS1ox) appears to occur in a diurnal cycle. These findings suggest that during the salinity stress response, the expression of RD29A and SOS1 is modulated by diurnal cycles and the circadian clock, which allows the plant to anticipate and respond effectively to daytime transpiration-triggered dehydration, drought, and salinity stress.