The carnivorous Venus flytrap uses prey-derived amino acid carbon to fuel respiration

Mechanosensor for Proprioception Inspired by Ultrasensitive Trigger Hairs of Venus Flytrap

Mechanosensors, as the core component of a proprioceptive system, can detect many types of mechanical signals in their surroundings, such as force signals, displacement signals, and vibration signals. It is understandable that the development of an all-new mechanosensory structure that can be widely used is highly desirable. This is because it can markedly improve the detection performance of mechanosensors. Coincidentally, in nature, optimized microscale trigger hairs of Venus flytrap are ingeniously used as a mechanosensory structure. These trigger hairs are utilized for tactile mechanosensilla to efficiently detect external mechanical stimuli. Biological trigger hair-based mechanosensilla offer an all-new bio-inspired strategy. This strategy utilizes the notch structure and variable stiffness to enhance the perceptual performance of mechanosensors. In this study, the structure-performance-application coupling relationship of trigger hair-based mechanosensors is explored through experiment and analysis. An artificial trigger hair-based mechanosensor is developed by mimicking the deformation properties of the Venus flytrap trigger hair. This bio-inspired mechanosensor shows excellent performance in terms of mechanical stability, response time, and sensitivity to mechanical signals.

Distinctive plastome evolution in carnivorous angiosperms

BACKGROUND

Independent origins of carnivory in multiple angiosperm families are fabulous examples of convergent evolution using a diverse array of life forms and habitats. Previous studies have indicated that carnivorous plants have distinct evolutionary trajectories of plastid genome (plastome) compared to their non-carnivorous relatives, yet the extent and general characteristics remain elusive.

RESULTS

We compared plastomes from 9 out of 13 carnivorous families and their non-carnivorous relatives to assess carnivory-associated evolutionary patterns. We identified inversions in all sampled Droseraceae species and four species of Utricularia, Pinguicula, Darlingtonia and Triphyophyllum. A few carnivores showed distinct shifts in inverted repeat boundaries and the overall repeat contents. Many ndh genes, along with some other genes, were independently lost in several carnivorous lineages. We detected significant substitution rate variations in most sampled carnivorous lineages. A significant overall substitution rate acceleration characterizes the two largest carnivorous lineages of Droseraceae and Lentibulariaceae. We also observe moderate substitution rates acceleration in many genes of Cephalotus follicularis, Roridula gorgonias, and Drosophyllum lusitanicum. However, only a few genes exhibit significant relaxed selection.

CONCLUSION

Our results indicate that the carnivory of plants have different effects on plastome evolution across carnivorous lineages. The complex mechanism under carnivorous habitats may have resulted in distinctive plastome evolution with conserved plastome in the Brocchinia hechtioides to strongly reconfigured plastomes structures in Droseraceae. Organic carbon obtained from prey and the efficiency of utilizing prey-derived nutrients might constitute possible explanation.

The digestive systems of carnivorous plants

To survive in the nutrient-poor habitats, carnivorous plants capture small organisms comprising complex substances not suitable for immediate reuse. The traps of carnivorous plants, which are analogous to the digestive systems of animals, are equipped with mechanisms for the breakdown and absorption of nutrients. Such capabilities have been acquired convergently over the past tens of millions of years in multiple angiosperm lineages by modifying plant-specific organs including leaves. The epidermis of carnivorous trap leaves bears groups of specialized cells called glands, which acquire substances from their prey via digestion and absorption. The digestive glands of carnivorous plants secrete mucilage, pitcher fluids, acids, and proteins, including digestive enzymes. The same (or morphologically distinct) glands then absorb the released compounds via various membrane transport proteins or endocytosis. Thus, these glands function in a manner similar to animal cells that are physiologically important in the digestive system, such as the parietal cells of the stomach and intestinal epithelial cells. Yet, carnivorous plants are equipped with strategies that deal with or incorporate plant-specific features, such as cell walls, epidermal cuticles, and phytohormones. In this review, we provide a systematic perspective on the digestive and absorptive capacity of convergently evolved carnivorous plants, with an emphasis on the forms and functions of glands.

Recent ecophysiological, biochemical and evolutional insights into plant carnivory

BACKGROUND

Carnivorous plants are an ecological group of approx. 810 vascular species which capture and digest animal prey, absorb prey-derived nutrients and utilize them to enhance their growth and development. Extant carnivorous plants have evolved in at least ten independent lineages, and their adaptive traits represent an example of structural and functional convergence. Plant carnivory is a result of complex adaptations to mostly nutrient-poor, wet and sunny habitats when the benefits of carnivory exceed the costs. With a boost in interest and extensive research in recent years, many aspects of these adaptations have been clarified (at least partly), but many remain unknown.

SCOPE

We provide some of the most recent insights into substantial ecophysiological, biochemical and evolutional particulars of plant carnivory from the functional viewpoint. We focus on those processes and traits in carnivorous plants associated with their ecological characterization, mineral nutrition, cost-benefit relationships, functioning of digestive enzymes and regulation of the hunting cycle in traps. We elucidate mechanisms by which uptake of prey-derived nutrients leads to stimulation of photosynthesis and root nutrient uptake.

CONCLUSIONS

Utilization of prey-derived mineral (mainly N and P) and organic nutrients is highly beneficial for plants and increases the photosynthetic rate in leaves as a prerequisite for faster plant growth. Whole-genome and tandem gene duplications brought gene material for diversification into carnivorous functions and enabled recruitment of defence-related genes. Possible mechanisms for the evolution of digestive enzymes are summarized, and a comprehensive picture on the biochemistry and regulation of prey decomposition and prey-derived nutrient uptake is provided.

Complexity and diversity of motion amplification and control strategies in motile carnivorous plant traps

Similar to animals, plants have evolved mechanisms for elastic energy storage and release to power and control rapid motion, yet both groups have been largely studied in isolation. This is exacerbated by the lack of consistent terminology and conceptual frameworks describing elastically powered motion in both groups. Iconic examples of fast movements can be found in carnivorous plants, which have become important models to study biomechanics, developmental processes, evolution and ecology. Trapping structures and processes vary considerably between different carnivorous plant groups. Using snap traps, suction traps and springboard-pitfall traps as examples, we illustrate how traps mix and match various mechanisms to power, trigger and actuate motions that contribute to prey capture, retention and digestion. We highlight a fundamental trade-off between energetic investment and movement control and discuss it in a functional-ecological context.

The effects of carbon dots produced by the Maillard reaction on the HepG2 cell substance and energy metabolism

Endogenous nanoparticles produced during food processing have received considerable attention due to their unique physicochemical properties and potential safety risks. However, the bio-impact of endogenous nanoparticles on cell metabolism has not been fully studied. In this work, the effects of carbon dots (CDs) derived from the Maillard reaction of glucose and lysine on the cellular substance and energy metabolism were assessed using HepG2 cells as a model. When the HepG2 cells were incubated with 10.0 mg mL-1 of CDs, the mitochondrial membrane potential decreased significantly and the mitochondrial function was affected. The extracellular acidification rate and oxygen consumption rate were decreased in comparison to normal cells without CDs. The CDs blocked the glycolysis pathway by reducing the activities of key enzymes including phosphofructokinase and pyruvate kinase. The energy supply pathway of HepG2 cells changed from glycolysis to TCA cycle, but the increase of the TCA cycle flux could not meet the requirements for restoring cell proliferation. The increase of the compensatory flux in the TCA cycle may be the result of up-regulation of the metabolism of glucogenic amino acids and ketogenic amino acids, while lipid metabolism did not seem to be affected in this process.

Snapping mechanics of the Venus flytrap (Dionaea muscipula)

The mechanical principles for fast snapping in the iconic Venus flytrap are not yet fully understood. In this study, we obtained time-resolved strain distributions via three-dimensional digital image correlation (DIC) for the outer and inner trap-lobe surfaces throughout the closing motion. In combination with finite element models, the various possible contributions of the trap tissue layers were investigated with respect to the trap's movement behavior and the amount of strain required for snapping. Supported by in vivo experiments, we show that full trap turgescence is a mechanical-physiological prerequisite for successful (fast and geometrically correct) snapping, driven by differential tissue changes (swelling, shrinking, or no contribution). These are probably the result of the previous accumulation of internal hydrostatic pressure (prestress), which is released after trap triggering. Our research leads to an in-depth mechanical understanding of a complex plant movement incorporating various actuation principles.

Photosynthetic cyclic electron transport provides ATP for homeostasis during trap closure in Dionaea muscipula

BACKGROUND AND AIMS

The processes connected with prey capture and the early consumption of prey by carnivorous Dionaea muscipula require high amounts of energy. The aim of the present study was to identify processes involved in flytrap energy provision and ATP homeostasis under these conditions.

METHODS

We determined photosynthetic CO2 uptake and chlorophyll fluorescence as well as the dynamics of ATP contents in the snap traps upon closure with and without prey.

KEY RESULTS

The results indicate that upon prey capture, a transient switch from linear to cyclic electron transport mediates a support of ATP homeostasis. Beyond 4 h after prey capture, prey resources contribute to the traps' ATP pool and, 24 h after prey capture, export of prey-derived resources to other plant organs may become preferential and causes a decline in ATP contents.

CONCLUSIONS

Apparently, the energy demand of the flytrap for prey digestion and nutrient mining builds on both internal and prey-derived resources.

Jasmonate signalling in carnivorous plants: copycat of plant defence mechanisms

The lipid-derived jasmonate phytohormones (JAs) regulate a wide spectrum of physiological processes in plants such as growth, development, tolerance to abiotic stresses, and defence against pathogen infection and insect attack. Recently, a new role for JAs has been revealed in carnivorous plants. In these specialized plants, JAs can induce the formation of digestive cavities and regulate enzyme production in response to different stimuli from caught prey. Appearing to be a new function for JAs in plants, a closer look reveals that the signalling pathways involved resemble known signalling pathways from plant defence mechanisms. Moreover, the digestion-related secretome of carnivorous plants is composed of many pathogenesis-related (PR) proteins and low molecular weight compounds, indicating that the plant carnivory syndrome is related to and has evolved from plant defence mechanisms. This review describes the similarities between defence and carnivory. It further describes how, after recognition of caught insects, JAs enable the carnivorous plants to digest and benefit from the prey. In addition, a causal connection between electrical and jasmonate signalling is discussed.

Plastome-Wide Rearrangements and Gene Losses in Carnivorous Droseraceae

The plastid genomes of four related carnivorous plants (Drosera regia, Drosera erythrorhiza, Aldrovanda vesiculosa, and Dionaea muscipula) were sequenced to examine changes potentially induced by the transition to carnivory. The plastid genomes of the Droseraceae show multiple rearrangements, gene losses, and large expansions or contractions of the inverted repeat. All the ndh genes are lost or nonfunctional, as well as in some of the species, clpP1, ycf1, ycf2 and some tRNA genes. Uniquely, among land plants, the trnK gene has no intron. Carnivory in the Droseraceae coincides with changes in plastid gene content similar to those induced by parasitism and mycoheterotrophy, suggesting parallel changes in chloroplast function due to the similar switch from autotrophy to (mixo-) heterotrophy. A molecular phylogeny of the taxa based on all shared plastid genes indicates that the "snap-traps" of Aldrovanda and Dionaea have a common origin.

Regulation of Hydrolytic Enzyme Activity in Aquatic Microbial Communities Hosted by Carnivorous Pitcher Plants

Carnivorous pitcher plants Sarracenia purpurea host diverse eukaryotic and bacterial communities which aid in insect prey digestion, but little is known about the functional processes mediated by the microbial communities. This study aimed to connect pitcher community diversity with functional nutrient transformation processes, identifying bacterial taxa, and measuring regulation of hydrolytic enzyme activity in response to prey and alternative nutrient sources. Genetic analysis identified diverse bacterial taxa known to produce hydrolytic enzyme activities. Chitinase, protease, and phosphatase activities were measured using fluorometric assays. Enzyme activity in field pitchers was positively correlated with bacterial abundance, and activity was suppressed by antibiotics suggesting predominantly bacterial sources of chitinase and protease activity. Fungi, algae, and rotifers observed could also contribute enzyme activity, but fresh insect prey released minimal chitinase activity. Activity of chitinase and proteases was upregulated in response to insect additions, and phosphatase activity was suppressed by phosphate additions. Particulate organic P in prey was broken down, appearing as increasing dissolved organic and inorganic P pools within 14 days. Chitinase and protease were not significantly suppressed by availability of dissolved organic substrates, though organic C and N stimulated bacterial growth, resulting in elevated enzyme activity. This comprehensive field and experimental study show that pitcher plant microbial communities dynamically regulate hydrolytic enzyme activity, to digest prey nutrients to simpler forms, mediating biogeochemical nutrient transformations and release of nutrients for microbial and host plant uptake.

Venus Flytrap: How an Excitable, Carnivorous Plant Works

The carnivorous plant Dionaea possesses very sensitive mechanoreceptors. Upon contact with prey an action potential is triggered which, via an electrical network - comparable to the nervous system of vertebrates - rapidly closes its bivalved trap. The 'hunting cycle' comprises a constitutively activated mechanism for the rapid capture of prey, followed by a well-orchestrated sequence of activation of genes responsible for tight trap closure, digestion of the prey, and uptake of nutrients. Decisions on the step-by-step activation are based on 'counting' the number of stimulations of sensory organs. These remarkable animal-like skills in the carnivore are achieved not by taking over genes from its prey but by modifying and rearranging the functions of genes that are ubiquitous in plants.

Triggering a false alarm: wounding mimics prey capture in the carnivorous Venus flytrap (Dionaea muscipula)

In the carnivorous plant Venus flytrap (Dionaea muscipula), the sequence of events after prey capture resembles the well-known plant defence signalling pathway in response to pathogen or herbivore attack. Here, we used wounding to mimic prey capture to show the similarities and differences between botanical carnivory and plant defence mechanisms. We monitored movement, electrical signalling, jasmonate accumulation and digestive enzyme secretion in local and distal (systemic) traps in response to prey capture, the mechanical stimulation of trigger hairs and wounding. The Venus flytrap cannot discriminate between wounding and mechanical trigger hair stimulation. Both induced the same action potentials, rapid trap closure, hermetic trap sealing, the accumulation of jasmonic acid (JA) and its isoleucine conjugate (JA-Ile), and the secretion of proteases (aspartic and cysteine proteases), phosphatases and type I chitinase. The jasmonate accumulation and enzyme secretion were confined to the local traps, to which the stimulus was applied, which correlates with the propagation of electrical signals and the absence of a systemic response in the Venus flytrap. In contrast to plant defence mechanisms, the absence of a systemic response in carnivorous plant may represent a resource-saving strategy. During prey capture, it could be quite expensive to produce digestive enzymes in the traps on the plant without prey.

Dynamics of amino acid redistribution in the carnivorous Venus flytrap (Dionaea muscipula) after digestion of 13 C/15 N-labelled prey

Amino acids represent an important component in the diet of the Venus flytrap (Dionaea muscipula), and supply plants with much needed nitrogen resources upon capture of insect prey. Little is known about the significance of prey-derived carbon backbones of amino acids for the success of Dionaea's carnivorous life-style. The present study aimed at characterizing the metabolic fate of ¹⁵ N and ¹³ C in amino acids acquired from double-labeled insect powder. We tracked changes in plant amino acid pools and their δ¹³ C- and δ¹⁵ N-signatures over a period of five weeks after feeding, as affected by contrasting feeding intensity and tissue type (i.e., fed and non-fed traps and attached petioles of Dionaea). Isotope signatures (i.e., δ¹³ C and δ¹⁵ N) of plant amino acid pools were strongly correlated, explaining 60% of observed variation. Residual variation was related to contrasting effects of tissue type, feeding intensity and elapsed time since feeding. Synthesis of nitrogen-rich transport compounds (i.e., amides) during peak time of prey digestion increased ¹⁵ N- relative to ¹³ C- abundances in amino acid pools. After completion of prey digestion, ¹³ C in amino acid pools was progressively exchanged for newly fixed ¹² C. The latter process was most evident for non-fed traps and attached petioles of plants that had received ample insect powder. We argue that prey-derived amino acids contribute to respiratory energy gain and loss of ¹³ CO₂ during conversion into transport compounds (i.e., 2 days after feeding), and that amino-nitrogen helps boost photosynthetic carbon gain later on (i.e., 5 weeks after feeding).