Circadian clocks provide a competitive advantage in an environment that is heavily influenced by the rotation of the Earth, by driving daily rhythms in behaviour, physiology and metabolism in ...bacteria, fungi, plants and animals. Circadian clocks comprise transcription-translation feedback loops, which are entrained by environmental signals such as light and temperature to adjust the phase of rhythms to match the local environment. The production of sugars by photosynthesis is a key metabolic output of the circadian clock in plants. Here we show that these rhythmic, endogenous sugar signals can entrain circadian rhythms in Arabidopsis thaliana by regulating the gene expression of circadian clock components early in the photoperiod, thus defining a 'metabolic dawn'. By inhibiting photosynthesis, we demonstrate that endogenous oscillations in sugar levels provide metabolic feedback to the circadian oscillator through the morning-expressed gene PSEUDO-RESPONSE REGULATOR 7 (PRR7), and we identify that prr7 mutants are insensitive to the effects of sucrose on the circadian period. Thus, photosynthesis has a marked effect on the entrainment and maintenance of robust circadian rhythms in A. thaliana, demonstrating that metabolism has a crucial role in regulation of the circadian clock.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The clockwork of plant circadian oscillators has been resolved through investigations in Arabidopsis thaliana. The circadian oscillator is an important regulator of much of plant physiology, though ...many of the mechanisms are unclear. New findings demonstrate that the oscillator adjusts phase and period in response to abiotic and biotic signals, providing insight in to how the plant circadian oscillator integrates with the biology of the cell and entrains to light, dark and temperature cycles. We propose that the plant circadian oscillator is dynamically plastic, in constant adjustment, rather than being an isolated clock impervious to cellular events.
Human health is dependent on a plentiful and nutritious supply of food, primarily derived from crop plants. Rhythmic supply of light as a result of the day and night cycle led to the evolution of ...circadian clocks that modulate most plant physiology, photosynthesis, metabolism, and development. To regulate crop traits and adaptation, breeders have indirectly selected for variation at circadian genes. The pervasive impact of the circadian system on crops suggests that future food production might be improved by modifying circadian rhythms, engineering the timing of transgene expression, and applying agricultural treatments at the most effective time of day. We describe the applied research required to take advantage of circadian biology in agriculture to increase production and reduce inputs.
Circadian clocks are believed to confer an advantage to plants, but the nature of that advantage has been unknown. We show that a substantial photosynthetic advantage is conferred by correct matching ...of the circadian clock period with that of the external light-dark cycle. In wild type and in long- and short-circadian period mutants of Arabidopsis thaliana, plants with a clock period matched to the environment contain more chlorophyll, fix more carbon, grow faster, and survive better than plants with circadian periods differing from their environment. This explains why plants gain advantage from circadian control.
Arabinogalactan proteins (AGPs) are a family of plant extracellular proteoglycans involved in many physiological events. AGPs are often anchored to the extracellular side of the plasma membrane and ...are highly glycosylated with arabinogalactan (AG) polysaccharides, but the molecular function of this glycosylation remains largely unknown. The β-linked glucuronic acid (GlcA) residues in AG polysaccharides have been shown in vitro to bind to calcium in a pH-dependent manner. Here, we used Arabidopsis (
) mutants in four AG β-glucuronyltransferases (GlcAT14A, -B, -D, and -E) to understand the role of glucuronidation of AG. AG isolated from
triple mutants had a strong reduction in glucuronidation. AG from a
triple mutant had lower calcium binding capacity in vitro than AG from wild-type plants. Some mutants had multiple developmental defects such as reduced trichome branching.
triple mutant plants had severely limited seedling growth and were sterile, and the propagation of calcium waves was perturbed in roots. Several of the developmental phenotypes were suppressed by increasing the calcium concentration in the growth medium. Our results show that AG glucuronidation is crucial for multiple developmental processes in plants and suggest that a function of AGPs might be to bind and release cell-surface apoplastic calcium.
Circadian clocks drive rhythmic physiology and metabolism to optimize plant growth and performance under daily environmental fluctuations caused by the rotation of the planet. Photosynthesis is a key ...metabolic process that must be appropriately timed to the light-dark cycle. The circadian clock contributes to the regulation of photosynthesis, and in turn the daily accumulation of sugars from photosynthesis also feeds back to regulate the circadian oscillator. We have previously shown that GIGANTEA (GI) is required to sustain Suc-dependent circadian rhythms in darkness. The mechanism by which Suc affects the circadian oscillator in a GI-dependent manner was unknown. Here, we identify that Suc sustains rhythms in the dark by stabilizing GI protein, dependent on the F-box protein ZEITLUPE, and implicate CONSTITUTIVE TRIPLE RESPONSE1 (CTR1), a negative regulator of ethylene signaling. Our identification of a role for CTR1 in the response to Suc prompted a reinvestigation of the effects of ethylene on the circadian oscillator. We demonstrate that ethylene shortens the circadian period, conditional on the effects of Suc and requiring GI. These findings reveal that Suc affects the stability of circadian oscillator proteins and can mask the effects of ethylene on the circadian system, identifying novel molecular pathways for input of sugar to the Arabidopsis (Arabidopsis thaliana) circadian network.
Circadian clocks are 24-h timing devices that phase cellular responses; coordinate growth, physiology, and metabolism; and anticipate the day-night cycle. Here we report sensitivity of the ...Arabidopsis thaliana circadian oscillator to sucrose, providing evidence that plant metabolism can regulate circadian function. We found that the Arabidopsis circadian system is particularly sensitive to sucrose in the dark. These data suggest that there is a feedback between the molecular components that comprise the circadian oscillator and plant metabolism, with the circadian clock both regulating and being regulated by metabolism. We used also simulations within a three-loop mathematical model of the Arabidopsis circadian oscillator to identify components of the circadian clock sensitive to sucrose. The mathematical studies identified GIGANTEA (GI) as being associated with sucrose sensing. Experimental validation of this prediction demonstrated that GI is required for the full response of the circadian clock to sucrose. We demonstrate that GI acts as part of the sucrose-signaling network and propose this role permits metabolic input into circadian timing in ARABIDOPSIS:
Circadian entrainment in Arabidopsis Wang, Shouming; Steed, Gareth; Webb, Alex A R
Plant physiology (Bethesda),
09/2022, Letnik:
190, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
Circadian clocks coordinate physiology and development as an adaption to the oscillating day/night cycle caused by the rotation of Earth on its axis and the changing length of day and night ...away from the equator caused by orbiting the sun. Circadian clocks confer advantages by entraining to rhythmic environmental cycles to ensure that internal events within the plant occur at the correct time with respect to the cyclic external environment. Advances in determining the structure of circadian oscillators and the pathways that allow them to respond to light, temperature, and metabolic signals have begun to provide a mechanistic insight to the process of entrainment in Arabidopsis (Arabidopsis thaliana). We describe the concepts of entrainment and how it occurs. It is likely that a thorough mechanistic understanding of the genetic and physiological basis of circadian entrainment will provide opportunities for crop improvement.
The mechanisms by which circadian clocks adjust to daily rhythms of light, dark, temperature, and internal metabolism are now coming to light.
• Changes in the spatiotemporal concentration of free Ca2+ (Ca2+) in different organelles of the cell contribute to responses of plants to physiological and environmental stimuli. One example are ...Ca2+ increases in the stroma of chloroplasts during light-to-dark transitions; however, the function and mechanisms responsible are unknown, in part because there is a disagreement in the literature concerning whether corresponding dark-induced changes in cytosolic Ca2+ (Ca2+cyt) can be detected.
• We have measured changes in Ca2+cyt upon darkness in addition to the already known dark-induced increases in Ca2+stroma in the aerial part of the Arabidopsis thaliana plant.
• These Ca2+cyt transients depend on the photoperiod and time of day, peaking at anticipated dusk, and are superimposed on daily 24 h oscillations in Ca2+cyt. We also find that the magnitude of the dark-induced increases in Ca2+ in both the cytosol and chloroplasts are gated by the nuclear circadian oscillator.
• The modulation of the magnitude of dark-induced increases in Ca2+stroma and Ca2+cyt by transcriptional regulators in the nucleus that are part of the circadian oscillator demonstrates a new role for the circadian system in subcellular Ca2+ signalling, in addition to its role in driving circadian oscillations of Ca2+ in the cytosol and chloroplasts.
Summary
Cucumber mosaic virus (CMV) encodes the 2b protein, which plays a role in local and systemic virus movement, symptom induction and suppression of RNA silencing. It also disrupts signalling ...regulated by salicylic acid and jasmonic acid. CMV induced an increase in tolerance to drought in Arabidopsis thaliana. This was caused by the 2b protein, as transgenic plants expressing this viral factor showed increased drought tolerance, but plants infected with CMVΔ2b, a viral mutant lacking the 2b gene, did not. The silencing effector ARGONAUTE1 (AGO1) controls a microRNA‐mediated drought tolerance mechanism and, in this study, we noted that plants (dcl2/3/4 triple mutants) lacking functional short‐interfering RNA‐mediated silencing were also drought tolerant. However, drought tolerance engendered by CMV may be independent of the silencing suppressor activity of the 2b protein. Although CMV infection did not alter the accumulation of the drought response hormone abscisic acid (ABA), 2b‐transgenic and ago1‐mutant seeds were hypersensitive to ABA‐mediated inhibition of germination. However, the induction of ABA‐regulated genes in 2b‐transgenic and CMV‐infected plants was inhibited more strongly than in ago1‐mutant plants. The virus engenders drought tolerance by altering the characteristics of the roots and not of the aerial tissues as, compared with the leaves of silencing mutants, leaves excised from CMV‐infected or 2b‐transgenic plants showed greater stomatal permeability and lost water more rapidly. This further indicates that CMV‐induced drought tolerance is not mediated via a change in the silencing‐regulated drought response mechanism. Under natural conditions, virus‐induced drought tolerance may serve viruses by aiding susceptible hosts to survive periods of environmental stress.
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