Circadian control of plant responses to drought

drought responses rely on ABA- dependent and ABA-independent pathways.

One of the main regulators of drought-stress signaling, cytosolic free [Ca2+], is regulated by the clock and integrates oscillator time with the envi- ronmental signals.
The stomatal aperture is able to anticipate the dawn and dusk signals
TOC1 and PRR7 are clock components that might be related to drought responses;GRP7 is highly expressed in guard cells and has a key role in the regulation of stomatal opening.

Role of the circadian clock regulating plant responses to high salinity

The molecular connection between the clock and plant responses to high salinity seems to rely on the circadian component GIGANTEA (GI), which confers high-salt tolerance through the control of the SALT OVERLY SENSITIVE (SOS) pathway.
Salt stresses also feed back to regulate the amplitude, period, and phase of the circadian clock

Circadian timing and cold-stress responses in plants Adaptation

The canonical cold-response pathway involves the CBF proteins which function as transcriptional activators of the so-called COLD REGULATED (COR) targets

CCA1 and LHY positively regulate CBF gene expression by binding directly to their promoters
The PRR9/7/5 proteins bind to the promoters of CBF genes and repress their transcription in a circadian-dependent manner
CBF1 regulates LUX transcription by binding directly to its promoter. The lux mutant seedlings are also sensitive to freezing stress
Alternative splicing is one mechanism by which temperature signals are transmitted to the clock by the cold-induced alternative splicing of LHY, PRR3, 5, 7, 9, and TOC1

Circadian control of plant immunity

the circadian clock has a key role dictating pathogen–host interactions and thereby contributing to enhanced plant fitness by balancing immune responses with cellular metabolism

arrhythmic plants with a dysfunctional clock such as CCA1 overexpressing plants (CCA1-ox) and elf3-1 mutants do not show the temporal variation in pathogen susceptibility
The expression of a large number of genes involved in PAMP perception is under the control of the circadian clock even in the absence of pathogen attacks.
The expres- sion of many R genes and their regulatory targets is also circadian-regulated
the RPP4 and a majority of its putative target genes have clock-related motifs in their promoters, and accordingly display rhythmic expression that largely over-laps with that of CCA1
- CCA1 directly activates RPP4 to facilitate a gradual and sustained expression of the target defense genes involved in PCD.
- CCA1 can also activate, via a distinctive diurnal phase, some RPP4-target genes independently of RPP4 for basal defense.
CCA1 and LHY contribute to plant defense through the circadian regulation of stomatal aperture

Defense hormone signaling

The accumulation of salicylic acid (SA) and jasmonic acid (JA) is clock-regulated: SA has a maximum accumulation at midnight, whereas JA peaks around midday, in tune with the corresponding pathogen behaviors.