The key clock component ZEITLUPE (ZTL) negatively regulates ABA signaling by degradation of CHLH in Arabidopsis.

Ubiquitination-mediated protein degradation plays important roles in ABA signal transduction and delivering responses to chloroplast stress signals in plants, but additional E3 ligases of protein ubiquitination remain to be identified to understand the complex signaling network. Here we reported that ZEITLUPE (ZTL), an F-box protein, negatively regulates abscisic acid (ABA) signaling during ABA-inhibited early seedling growth and ABA-induced stomatal closure in . Using molecular biology and biochemistry approaches, we demonstrated that ZTL interacts with and ubiquitinates its substrate, CHLH/ABAR (Mg-chelatase H subunit/putative ABA receptor), to modulate CHLH stability via the 26S proteasome pathway.

The functional interplay between protein kinase CK2 and CCA1 transcriptional activity is essential for clock temperature compensation in Arabidopsis.

Circadian rhythms are daily biological oscillations driven by an endogenous mechanism known as circadian clock. The protein kinase CK2 is one of the few clock components that is evolutionary conserved among different taxonomic groups. CK2 regulates the stability and nuclear localization of essential clock proteins in mammals, fungi, and insects.

A functional connection between the clock component TOC1 and abscisic acid signaling pathways.

The hormone abscisic acid (ABA) regulates the stress signals crucial for plant tolerance to adverse environmental conditions. The circadian clock also uses environmental cues for appropriate timing of plant physiology and metabolism. Despite previous studies showing the connections between ABA and clock signalling pathways, the molecular nodes underlying these connections remained unknown.

Interaction of shade avoidance and auxin responses: a role for two novel atypical bHLH proteins.

Plants sense the presence of potentially competing nearby individuals as a reduction in the red to far-red ratio of the incoming light. In anticipation of eventual shading, a set of plant responses known as the shade avoidance syndrome (SAS) is initiated soon after detection of this signal by the phytochrome photoreceptors. Here we analyze the function of PHYTOCHROME RAPIDLY REGULATED1 (PAR1) and PAR2, two Arabidopsis thaliana genes rapidly upregulated after simulated shade perception.

Altered oscillator function affects clock resonance and is responsible for the reduced day-length sensitivity of CKB4 overexpressing plants.

Most organisms have evolved a timing mechanism or circadian clock that is able to generate 24 h rhythmic oscillations in multiple biological events. The environmental fluctuations in light and temperature synchronize the expression and activity of key oscillator components that ultimately define the period, phase and amplitude of output rhythms. In Arabidopsis, overexpression of the casein kinase 2 (CK2) regulatory subunits, CKB3 or CKB4, alters the function of the clock under free-running conditions, and results in period-shortening of genes peaking at different phase angles.

The proteasome-dependent degradation of CKB4 is regulated by the Arabidopsis biological clock.

Most organisms have evolved an internal timing mechanism, the circadian clock, that is able to generate and maintain 24 h rhythmic oscillation in molecular, biochemical and metabolic activities. In Arabidopsis, the clock-dependent synchronization of physiology with the environment is essential for successful growth and development. The mechanisms of the Arabidopsis clockwork have been described as transcriptional feedback loops at the core of the oscillator.