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In: phys.org
Excerpts:"How does the plant protect its vital snap traps and sensory hairs from fire? Biophysicists Professor Rainer Hedrich and Dr. Shouguang Huang from Julius-Maximilians-University (JMU) Würzburg in Bavaria, Germany, have found out: The Venus flytrap uses special heat receptors in the sensory hairs for this purpose, as the researchers report in the journal Current Biology."
"He found that when a local leaf temperature of 37°C was exceeded, the heated area of the trap produced an electrical impulse, an action potential that spread across both halves of the trap. "When the temperature increased further to 55°C, a second action potential was triggered and the trap snapped shut," Shouguang said. But the trap's reaction at 37°C and 55°C only kicked in when temperatures increased abruptly, as in a rapid heat wave. If the temperature rose only slowly, as on hot summer days, the traps did not react."
"Each half of the trap has three sensory hairs that are highly sensitive to touch and generate action potentials. The action potentials are generated at the base of the hairs. There, ion channels that get activated by touch allow calcium to flow into the cells. This calcium signal is the trigger and at the same time an integral part of an action potential. Heat jumps cause the same calcium-dependent electrical events in the sensory hairs as touch."
Authors: Trupti Gaikwad, Susan Breen, Emily Breeze, Rana M. Fraz Hussain, Satish Kulasekaran, Marta de Torres-Zabala, David Horsell, Lorenzo Frigerio and Murray Grant.
bioRxiv (2023)
Abstract: "Successful recognition of pathogen effectors by plant disease resistance proteins (effector triggered immunity, ETI) contains the invading pathogen through a localized hypersensitive response (HR). In addition, ETI activates long-range signalling cascades that establish broad spectrum systemic acquired resistance (SAR). Using a novel and sensitive reporter we have been able to image the spatio- temporal dynamics of SAR. We demonstrate that local ETI triggered SAR signal generation, followed by rapid propagation and establishment in systemic responding leaves, is dependent on both jasmonate biosynthesis and perception. Further, ETI initiates calcium- and jasmonate-dependent systemic surface electrical potentials, reminiscent of those activated by herbivory but with slower propagation kinetics. Thus, jasmonate signalling is crucial to the initiation and establishment of systemic defence responses against a diverse range of phytopathogens."
Authors: Takuma Hagihara, Hiroaki Mano, Tomohiro Miura, Mitsuyasu Hasebe and Masatsugu Toyota.
Nature Communications (2022)
Editor's view: Mimosa pudica moves its leaves within seconds of being touched or wounded. Here the authors show that such movements are triggered by rapid changes in Ca2+ and action and variation potentials and provide evidence that rapid movements help protect the plant from insect attacks.
Abstract: "Animals possess specialized systems, e.g., neuromuscular systems, to sense the environment and then move their bodies quickly in response. Mimosa pudica, the sensitive plant, moves its leaves within seconds in response to external stimuli; e.g., touch or wounding. However, neither the plant-wide signaling network that triggers these rapid movements nor the physiological roles of the movements themselves have been determined. Here by simultaneous recording of cytosolic Ca2+ and electrical signals, we show that rapid changes in Ca2+ coupled with action and variation potentials trigger rapid movements in wounded M. pudica. Furthermore, pharmacological manipulation of cytosolic Ca2+ dynamics and CRISPR-Cas9 genome editing technology revealed that an immotile M. pudica is more vulnerable to attacks by herbivorous insects. Our findings provide evidence that rapid movements based on propagating Ca2+ and electrical signals protect this plant from insect attacks."
Authors: Jennifer Böhm and Sönke Scherzer.
Plant Physiology (2021)
One-sentence summary: Origin and molecular basis of plant electrical signal transmission with associated downstream processes exemplified by the hunting cycle of the Venus flytrap.
Excerpts: "Plant long-distance electrical signalling events in response to environmental stimuli are widely described in three different manifestations: i) variation potentials (VPs; these highly variable signals are also called electro-potential waves or slow wave potentials (SWPs)), ii) system potentials (SPs) and iii) APs."
"Of these three electrical signals, APs propagate most rapidly within the plant body, with typical propagation speeds calculated in the centimetre-per-second range (Volkov et al., 2008, Vodeneev et al., 2015).
"Because of these robust APs, a great deal of work on electrical signals in plants has been done on the Venus flytrap. In this review, we therefore focus on carnivorous examples from the plant electrical signalling literature and following membrane transport mechanisms underlying the carnivorous lifestyle, including prey recognition and capture, digestion, and nutrient uptake."
"Mimicking a series (more than three) of trigger-hair stimulations, the JA signalling pathway is induced, mediating the expression of genes encoding prey-degrading hydrolases in the secretory gland cells."
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Authors: Shouguang Huang and Rainer Hedrich.
Current Biology (2023)
Editor's view: Huang and Hedrich demonstrate that Venus flytraps can recognize heat waves and close in the forefront of fires using a trigger-hair-localized thermo-electrical alarm system. Upon calcium-electrical excitation, the traps close, protecting the vulnerable trigger hairs from burning and enabling them to resume capturing prey after the fire has passed.
Highlights: • The trigger hair podium converts thermal energy into a propagating Ca2+ wave • Heat provokes action potentials and Ca2+ waves, which initiate flytrap closure • Flytrap's thermosensor detects critical temperatures and the rise-time velocity • Heat sensor is primed to sense the change rather than absolute temperature
Abstract: "Most plants suffer greatly from heat in general and fire in particular, but some can profit from what is called fire ecology.1 Dionaea muscipula, the Venus flytrap, is one such plant. In its natural habitat in the Green Swamps, Dionaea often faces challenges from excessive growth of grass and evergreen shrubs that overshadow the plant.2 Without natural fire, the Dionaea populations would decline.3 How does Dionaea survive and even thrive after swamp fires? Here, we ask whether flytraps recognize heat waves at the forefront of swamp fires and demonstrate that a heat-sensor-based alarm may provide a fire survival strategy for them. In this study, we show that flytraps become electrically excited and close in response to a heat wave. Over a critical temperature of 38°C, traps fire action potentials (APs), which are interconnected with cytosolic Ca2+ transients. The heat-induced Ca2+-AP has a 3-min refractory period, yet traps still respond to cold, voltage, and glutamate. The heat responses were trap specific, emerging only when the trap became excitable. Upon heat stimulation, the Ca2+ wave originates in the trigger hair podium, indicating that the mechanosensory zone serves as a heat receptor organ. In contrast to the human heat receptor, the flytrap sensor detects temperature change rather than the absolute body temperature. We propose that by sensing the temperature differential, flytraps can recognize the heat of an approaching fire, thus closing before the trigger hairs are burned, while they can continue to catch prey throughout hot summers."
Authors: Anda-Larisa Iosip, Sönke Scherzer, Sonja Bauer, Dirk Becker, Markus Krischke, Khaled A.S.Al-Rasheid, Jörg Schultz, Ines Kreuzer and Rainer Hedrich.
Current Biology (2023)
Editor's view: DYSCALCULIA is a Venus flytrap mutant that is still able to fire touch-induced action potentials but does not snap close its traps and fails to enter the hunting cycle. Iosip et al. demonstrate that this mutant cannot properly read, count, and decode touch-induced calcium signals that are key in prey capture and processing.
Highlights: • The Dionaea mutant DYSC fires action potentials but does not snap close its traps • DYSC exhibits defects in trap-restricted calcium- and JA-associated processes • Touch-activation of calcium signaling is largely suppressed in DYSC traps • DYSC is impaired in decoding touch-/action potential-induced calcium signals
Abstract: "The Venus flytrap Dionaea muscipula estimates prey nutrient content by counting trigger hair contacts initiating action potentials (APs) and calcium waves traveling all over the trap.1,2,3 A first AP is associated with a subcritical rise in cytosolic calcium concentration, but when the second AP arrives in time, calcium levels pass the threshold required for fast trap closure. Consequently, memory function and decision-making are timed via a calcium clock.3,4 For higher numbers of APs elicited by the struggling prey, the Ca2+ clock connects to the networks governed by the touch hormone jasmonic acid (JA), which initiates slow, hermetic trap sealing and mining of the animal food stock.5 Two distinct phases of trap closure can be distinguished within Dionaea’s hunting cycle: (1) very fast trap snapping requiring two APs and crossing of a critical cytosolic Ca2+ level and (2) JA-dependent slow trap sealing and prey processing induced by more than five APs. The Dionaea mutant DYSC is still able to fire touch-induced APs but does not snap close its traps and fails to enter the hunting cycle after prolonged mechanostimulation. Transcriptomic analyses revealed that upon trigger hair touch/AP stimulation, activation of calcium signaling is largely suppressed in DYSC traps. The observation that external JA application restored hunting cycle progression together with the DYSC phenotype and its transcriptional landscape indicates that DYSC cannot properly read, count, and decode touch/AP-induced calcium signals that are key in prey capture and processing."
Authors: Carl Procko, Ivan Radin, Charlotte Hou, Ryan A. Richardson, Elizabeth S. Haswell and Joanne Chory.
PNAS (2022)
Abstract: "Some of the most spectacular examples of botanical carnivory—in which predator plants catch and digest animals presumably to supplement the nutrient-poor soils in which they grow—occur within the Droseraceae family. For example, sundews of the genus Drosera have evolved leaf movements and enzyme secretion to facilitate prey digestion. The molecular underpinnings of this behavior remain largely unknown; however, evidence suggests that prey-induced electrical impulses are correlated with movement and production of the defense hormone jasmonic acid (JA), which may alter gene expression. In noncarnivorous plants, JA is linked to electrical activity via changes in cytoplasmic Ca2+. Here, we find that dynamic Ca2+ changes also occur in sundew (Drosera spatulata) leaves responding to prey-associated mechanical and chemical stimuli. Furthermore, inhibition of these Ca2+ changes reduced expression of JA target genes and leaf movements following chemical feeding. Our results are consistent with the presence of a conserved Ca2+-dependent JA signaling pathway in the sundew feeding response and provide further credence to the defensive origin of plant carnivory."
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