The Circadian Clock inCAMPlants

Abstract

The sections in this article areIntroductionThe Daily Cycle of Metabolism inCAMPlantsPhase Responses ofCAM CO2RhythmsThe Biochemical Basis for the Circadian Rhythm ofCO2FixationMultiple Points of Clock Control within theCAMPathway?The Molecular Identity of the Central Oscillator inCAMSpecies?Future Perspectives and Unanswered QuestionsAcknowledgements

Kalanchoë PPC1 Is Essential for Crassulacean Acid Metabolism and the Regulation of Core Circadian Clock and Guard Cell Signaling Genes

“…The circadian rhythm of CO 2 fixation observed for CAM species of Kalanchoë under constant free-running conditions is a classic example of a plant clock output rhythm driven by the underlying multi-gene-loop, autoregulatory core oscillator mechanism in the nucleus that sets the time (Hartwell, 2006). Under continuous light and temperature (LL) conditions, the CAM-associated circadian rhythm of CO 2 fixation dampened towards almost complete arrhythmia in detached leaves and whole, young plants of rPPC1-B, and CO 2 was fixed continuously ( Figure 6A and 6B).…”

“…Various Kalanchoë species display a persistent and robust circadian rhythm of CO 2 exchange when detached CAM leaves are measured with their petiole in distilled water (Wilkins, 1959). This discovery led to the current understanding that the endogenous circadian clock underpins the optimised temporal control of CAM in Kalanchoë (Hartwell, 2006;Boxall et al, 2017). The circadian rhythm of CO 2 exchange was measured for wild type, rPPC1-A and rPPC1-B using both detached LP6 sampled from 4-month-old mature plants and intact young plants at the 9-leafpairs stage (2 months old).…”

“…Crassulacean acid metabolism (CAM) is a pathway of photosynthetic CO 2 fixation found in species adapted to low rainfall and/or periodic drought, such as the CO 2 is re-fixed by RuBisCO behind closed stomata (Borland et al, 2009). Strict temporal control prevents a futile cycle between the enzymes and metabolite transporters driving malate production in the dark and those driving malate decarboxylation in the light (Hartwell, 2006). PPC regulation is central to this temporal control.…”

Conservation and Diversification of Circadian Rhythmicity Between a Model Crassulacean Acid Metabolism Plant Kalanchoë fedtschenkoi and a Model C3 Photosynthesis Plant Arabidopsis thaliana

“…It is widely accepted that CAM photosynthesis plants have evolved from C 3 photosynthesis plants ( Yang et al, 2015 , 2017 ; Yin et al, 2018 ). CAM photosynthesis results in improved photosynthetic and water-use efficiency, relative to C 3 photosynthesis, and it is hypothesized that the strict temporal control of CAM processes is maintained by the circadian clock in CAM plants ( Wyka et al, 2004 ; Boxall et al, 2005 ; Hartwell, 2005 , 2006 ; von Caemmerer and Griffiths, 2009 ; Ming et al, 2015 ). Evidence from several levels of biology have been reported supporting this hypothesis.…”

Crassulacean acid metabolism guard cell anion channel activity follows transcript abundance and is suppressed by apoplastic malate

“…They achieve these savings by initially fixing atmospheric CO 2 in the dark into Mal for storage in the mesophyll vacuole; they release and decarboxylate the stored Mal in the light for refixation by RuBisCO. CAM avoids futile cycling by temporal separation and optimisation of primary and secondary CO 2 fixation via transcriptional, translational and post-translational control of key metabolic enzymes and transporters in the mesophyll (Hartwell, 2006;Abraham et al, 2016;Boxall et al, 2017;Yang et al, 2017).…”