A carnivorous sundew plant prefers protein over chitin as a source of nitrogen from its traps

Complex transcription regulation of acidic chitinase suggests fine-tuning of digestive processes in Drosera binata

MAIN CONCLUSION

DbChitI-3, Drosera binata's acidic chitinase, peaks at pH 2.5 from 15 °C to 30 °C. Gene expression is stimulated by polysaccharides and suppressed by monosaccharide digestion, implying a feedback loop in its transcriptional regulation. Here, we characterised a novel chitinase gene (DbChitI-3) isolated from the carnivorous plant species Drosera binata with strong homology to other Drosera species' extracellular class I chitinases with a role in digestive processes. The capability to cleave different forms of chitin was tested using recombinantly produced chitinase in Escherichia coli (rDbChitI-3S-His) and subsequent purification. The recombinant protein did not cleave chitin powder, the mono-, di- and tri- N-acetyl-D-glucosamine substrates, but cleaved acetic acid-swollen chitin. Fluorometric assay with acetic acid-swollen FITC-chitin as a substrate revealed the maximum enzyme activity at pH 2.5, spanning from 15 °C to 30 °C. Comparing enzymatic parameters with commercial chitinase from Streptomyces griseus showed rDbChitI-3S-His efficiency reaching 64.3% of S. griseus chitinase under optimal conditions. The highest basal expression of DbChitI-3 was detected in leaf blades. In other organs, the expression was either fivefold lower (petioles) or almost nondetectable (stems, roots and flowers). Application of gelatin, chitin, and pachyman resulted in a 3.9-, 4.6- and 5.7-fold increase in the mRNA transcript abundance of DbChitI-3 in leaves. In contrast, monosaccharides and laminarin decreased transcription of the DbChitI-3 gene by at least 70%, 5 h after treatment. The simultaneous application of suppressor and inducer (glucose and pachyman) indicated the predominant effect of the suppressor, implying that sufficient monosaccharide nutrients prioritize absorption processes in D. binata leaves over further digestion of the potential substrate.

Prey capture by the non-native carnivorous pitcher plant Sarracenia purpurea across sites in Britain and Ireland

The carnivorous pitcher plant Sarracenia purpurea is native to North America, but has been introduced into Europe, where it is now widespread. Understanding of how this species functions in its non-native range is limited. We measured pitcher morphology and prey capture by S. purpurea in its non-native range in Britain and Ireland. Pitchers were removed from different plants at each of six bogs covering the species range in Britain and Ireland (n = 10 pitchers per site). For each pitcher we counted and identified every prey item and took measurements of morphology. We also compiled prey capture data for existing studies in Europe and North America. Prey capture characteristics varied between sites in Britain and Ireland. The amount of prey captured varied 20-fold between sites and was partially explained by differences in pitcher size; larger pitchers caught more prey. The primary prey was Formicidae, Diptera and Coleoptera. At the rank of order, prey composition varied between bogs, some contained mainly Formicidae, some mainly Diptera and some a mix. Prey capture was less evenly distributed at some bogs compared to others, suggesting more specialization. There was no overall difference in prey capture (composition or evenness) at the rank of order between plants in Europe compared to those in North America. At the rank of species, prey capture varied between populations even within the same order. This study demonstrates a large amount of variability between sites in prey capture characteristics. This may reflect different site characteristics and/or plant strategies, which will likely impact plant function, and may impact the inquiline community. In terms of prey capture at the rank of order, S. purpurea functions identically in its non-native range. This supports its use as a model system in a natural experiment for understanding food webs.

Snatching Sundews-Analysis of Tentacle Movement in Two Species of Drosera in Terms of Response Rate, Response Time, and Speed of Movement

Drosera, Droseraceae, catch prey with sticky tentacles. Both Australian Drosera allantostigma and widespread D. rotundifolia show three types of anatomically different tentacles: short, peripheral, and snap-tentacles. The latter two are capable of fast movement. This motion was analysed after mechanical, chemical, and electrical stimulation with respect to response rate, response time, and angular velocity of bending. Compared to D. rotundifolia, D. allantostigma responds more frequently and faster; the tentacles bend with higher angular velocity. Snap-tentacles have a lower response rate, shorter response time, and faster angular velocity. The response rates for chemical and electrical stimuli are similar, and higher than the rates for mechanical stimulus. The response time is not dependent on stimulus type. The higher motility in D. allantostigma indicates increased dependence on mechanical prey capture, and a reduced role of adhesive mucilage. The same tentacle types are present in both species and show similar motility patterns. The lower response rate of snap-tentacles might be a safety measure against accidental triggering, since the motion of snap-tentacles is irreversible and tissue destructive. Furthermore, tentacles seem to discern stimuli and respond specifically. The established model of stereotypical tentacle movement may not fully explain these observations.

Recent Progress on Plant-Inspired Soft Robotics with Hydrogel Building Blocks: Fabrication, Actuation and Application

Millions of years’ evolution has imparted life on earth with excellent environment adaptability. Of particular interest to scientists are some plants capable of macroscopically and reversibly altering their morphological and mechanical properties in response to external stimuli from the surrounding environment. These intriguing natural phenomena and underlying actuation mechanisms have provided important design guidance and principles for man-made soft robotic systems. Constructing bio-inspired soft robotic systems with effective actuation requires the efficient supply of mechanical energy generated from external inputs, such as temperature, light, and electricity. By combining bio-inspired designs with stimuli-responsive materials, various intelligent soft robotic systems that demonstrate promising and exciting results have been developed. As one of the building materials for soft robotics, hydrogels are gaining increasing attention owing to their advantageous properties, such as ultra-tunable modulus, high compliance, varying stimuli-responsiveness, good biocompatibility, and high transparency. In this review article, we summarize the recent progress on plant-inspired soft robotics assembled by stimuli-responsive hydrogels with a particular focus on their actuation mechanisms, fabrication, and application. Meanwhile, some critical challenges and problems associated with current hydrogel-based soft robotics are briefly introduced, and possible solutions are proposed. We expect that this review would provide elementary tutorial guidelines to audiences who are interested in the study on nature-inspired soft robotics, especially hydrogel-based intelligent soft robotic systems.

Enzyme activities in two sister-species of carnivorous pitcher plants (Nepenthes) with contrasting nutrient sequestration strategies

The carnivorous pitcher plants of the genus Nepenthes usually attract, capture and digest arthropod prey to obtain mineral nutrients. But few members of the genus have evolved specialized nutrient sequestration strategies to acquire nitrogen from the faeces and urine of mutualistic mammals, which they attract. Because the plants obtain significant amounts of nitrogen in a more available form, we hypothesized that they have relaxed the production of digestive enzymes. If so, species that digest mammal faeces should show fewer digestive enzymes than closely related species that rely on arthropods. We tested this hypothesis by comparing digestive enzymes in 1) Nepenthes hemsleyana, whose pitchers serve as roosts for the mutualistic woolly bat Kerivoula hardwickii, which also defecate inside the pitchers, and 2) the close relative Nepenthes rafflesiana, a typical arthropod capturing species. To investigate the dynamics of aspartic proteases (nepenthesin I and II) and type III and IV chitinases in both species, we conducted qPCR, western blotting, mass spectrometry, and enzyme activity measurements. We found that mRNA in pitcher tissue and enzyme abundance in the digestive fluid is upregulated in both species in response to faeces and insect feeding. Contrary to our initial hypothesis, the final nepenthesin proteolytic activity in the digestive fluid is higher in response to faeces addition than to insect prey irrespective of Nepenthes species. This indicates that faeces can mimic arthropod prey triggering the production of digestive enzymes and N. hemsleyana retained capacity for production of them.

Biochemical and mesophyll diffusional limits to photosynthesis are determined by prey and root nutrient uptake in the carnivorous pitcher plant Nepenthes × ventrata

BACKGROUND AND AIMS

Carnivorous plants can enhance photosynthetic efficiency in response to prey nutrient uptake, but the underlying mechanisms of increased photosynthesis are largely unknown. Here we investigated photosynthesis in the pitcher plant Nepenthes × ventrata in response to different prey-derived and root mineral nutrition to reveal photosynthetic constrains.

METHODS

Nutrient-stressed plants were irrigated with full inorganic solution or fed with four different insects: wasps, ants, beetles or flies. Full dissection of photosynthetic traits was achieved by means of gas exchange, chlorophyll fluorescence and immunodetection of photosynthesis-related proteins. Leaf biochemical and anatomical parameters together with mineral composition, nitrogen and carbon isotopic discrimination of leaves and insects were also analysed.

KEY RESULTS

Mesophyll diffusion was the major photosynthetic limitation for nutrient-stressed Nepenthes × ventrata, while biochemistry was the major photosynthetic limitation after nutrient application. The better nutrient status of insect-fed and root-fertilized treatments increased chlorophyll, pigment-protein complexes and Rubisco content. As a result, both photochemical and carboxylation potential were enhanced, increasing carbon assimilation. Different nutrient application affected growth, and root-fertilized treatment led to the investment of more biomass in leaves instead of pitchers.

CONCLUSIONS

The study resolved a 35-year-old hypothesis that carnivorous plants increase photosynthetic assimilation via the investment of prey-derived nitrogen in the photosynthetic apparatus. The equilibrium between biochemical and mesophyll limitations of photosynthesis is strongly affected by the nutrient treatment.

Taste for protein: Chemical signal from prey stimulates enzyme secretion through jasmonate signalling in the carnivorous plant Venus flytrap

Hunting cycle of the carnivorous plant Venus flytrap (Dionaea muscipula Ellis) is comprised of mechanism for rapid trap closure followed by slow hermetical sealing and activation of gene expression responsible for digestion of prey and nutrient uptake. In the present study, we focus on the late phase of Venus's flytrap hunting cycle when mechanical stimulation of the prey ceases and is replaced by chemical cues. We used two nitrogen-rich compounds (chitin and protein) in addition to mechanostimulation to investigate the electrical and jasmonate signalling responsible for induction of enzyme activities. Chemical stimulation by BSA protein and chitin did not induce any additional spontaneous action potentials (APs). However, chemical stimulation by protein induced the highest levels of jasmonic acid (JA) and its isoleucine conjugate (JA-Ile) as well as the expression of studied gene encoding a cysteine protease (dionain). Although chitin is probably the first chemical agent which is in direct contact with digestive glands, presence of protein in the secured trap mimics the presence of insect prey best.

Mechanistic Insight into the Binding and Swelling Functions of Prepeptidase C-Terminal (PPC) Domains from Various Bacterial Proteases

The bacterial prepeptidase C-terminal (PPC) domain can be found in the C termini of a wide variety of proteases that are secreted by marine bacteria. However, the functions of these PPC domains remain unknown due to a lack of systematic research. Here, the binding and swelling abilities of eight PPC domains from six different proteases were compared systematically via scanning electron microscopy (SEM), enzyme assays, and fluorescence spectroscopy. These PPC domains all possess the ability to bind and swell insoluble collagen. PPC domains can expose collagen monomers but cannot disrupt the pyridinoline cross-links or unwind the collagen triple helix. This ability can play a synergistic role alongside collagenase in collagen hydrolysis. Site-directed mutagenesis of the PPC domain from Vibrio anguillarum showed that the conserved polar and aromatic residues Y6, D26, D28, Y30, W42, E53, C55, and Y65 and the hydrophobic residues V10, V18, and I57 played key roles in substrate binding. Molecular dynamic simulations were conducted to investigate the interactions between PPC domains and collagen. Most PPC domains have a similar mechanism for binding collagen, and the hydrophobic binding pocket of PPC domains may play an important role in collagen binding. This study sheds light on the substrate binding mechanisms of PPC domains and reveals a new function for the PPC domains of bacterial proteases in substrate degradation.IMPORTANCE Prepeptidase C-terminal (PPC) domains commonly exist in the C termini of marine bacterial proteases. Reports examining PPC have been limited, and its functions remain unclear. In this study, eight PPCs from six different bacteria were examined. Most of the PPCs possessed the ability to bind collagen, feathers, and chitin, and all PPCs could significantly swell insoluble collagen. PPCs can expose collagen monomers but cannot disrupt pyridinoline cross-links or unwind the collagen triple helix. This swelling ability may also play synergistic roles in collagen hydrolysis. Comparative structural analyses and the examination of PPC mutants revealed that the hydrophobic binding pockets of PPCs may play important roles in collagen binding. This study provides new insights into the functions and ecological significance of PPCs, and the molecular mechanism of the collagen binding of PPCs was clarified, which is beneficial for the protein engineering of highly active PPCs and collagenase in the pharmaceutical industry and of artificial biological materials.

Regulation of enzyme activities in carnivorous pitcher plants of the genus Nepenthes

Nepenthes regulates enzyme activities by sensing stimuli from the insect prey. Protein is the best inductor mimicking the presence of an insect prey. Carnivorous plants of the genus Nepenthes have evolved passive pitcher traps for prey capture. In this study, we investigated the ability of chemical signals from a prey (chitin, protein, and ammonium) to induce transcription and synthesis of digestive enzymes in Nepenthes × Mixta. We used real-time PCR and specific antibodies generated against the aspartic proteases nepenthesins, and type III and type IV chitinases to investigate the induction of digestive enzyme synthesis in response to different chemical stimuli from the prey. Transcription of nepenthesins was strongly induced by ammonium, protein and live prey; chitin induced transcription only very slightly. This is in accordance with the amount of released enzyme and proteolytic activity in the digestive fluid. Although transcription of type III chitinase was induced by all investigated stimuli, a significant accumulation of the enzyme in the digestive fluid was found mainly after protein and live prey addition. Protein and live prey were also the best inducers for accumulation of type IV chitinase in the digestive fluid. Although ammonium strongly induced transcription of all investigated genes probably through membrane depolarization, strong acidification of the digestive fluid affected stability and abundance of both chitinases in the digestive fluid. The study showed that the proteins are universal inductors of enzyme activities in carnivorous pitcher plants best mimicking the presence of insect prey. This is not surprising, because proteins are a much valuable source of nitrogen, superior to chitin. Extensive vesicular activity was observed in prey-activated glands.

Occurrence of myo-inositol and alkyl-substituted polysaccharide in the prey-trapping mucilage of Drosera capensis

The chemical composition of the exudate mucilage droplets of the carnivorous plant Drosera capensis was investigated using nuclear magnetic resonance spectroscopy. The mucilage was found to contain beside a very large molecular weight polysaccharide a significant amount of myo-inositol. It appears that myo-inositol escaped detection due to the commonly applied methodology on the chemical analysis of plant mucilage, such as dialysis, precipitation of polysaccharide component with alcohol, acid hydrolysis and detection of the resultant monosaccharide (aldose) units. The possible functions of myo-inositol in the mucilage droplets and the fate after being washed off from the leaf tentacles are proposed. On the polysaccharide component, the presence of methyl ester and alkyl chain-like moieties could be confirmed. These lipophilic moieties may provide the prey-trapping mucilage with the unique adhesive property onto the hydrophobic insect body parts, as well as onto the nature's well-known superhydrophobic surfaces such as the leaves of the sacred lotus plants. A re-evaluation of the mineral components of the mucilage, reported 40 years ago, is presented from the viewpoints of the current result and plants' natural habitat. A case for re-examination of the well-studied plant mucilaginous materials is made in light of the new findings.

Structure prediction and network analysis of chitinases from the Cape sundew, Drosera capensis

BACKGROUND

Carnivorous plants possess diverse sets of enzymes with novel functionalities applicable to biotechnology, proteomics, and bioanalytical research. Chitinases constitute an important class of such enzymes, with future applications including human-safe antifungal agents and pesticides. Here, we compare chitinases from the genome of the carnivorous plant Drosera capensis to those from related carnivorous plants and model organisms.

METHODS

Using comparative modeling, in silico maturation, and molecular dynamics simulation, we produce models of the mature enzymes in aqueous solution. We utilize network analytic techniques to identify similarities and differences in chitinase topology.

RESULTS

Here, we report molecular models and functional predictions from protein structure networks for eleven new chitinases from D. capensis, including a novel class IV chitinase with two active domains. This architecture has previously been observed in microorganisms but not in plants. We use a combination of comparative and de novo structure prediction followed by molecular dynamics simulation to produce models of the mature forms of these proteins in aqueous solution. Protein structure network analysis of these and other plant chitinases reveal characteristic features of the two major chitinase families.

GENERAL SIGNIFICANCE

This work demonstrates how computational techniques can facilitate quickly moving from raw sequence data to refined structural models and comparative analysis, and to select promising candidates for subsequent biochemical characterization. This capability is increasingly important given the large and growing body of data from high-throughput genome sequencing, which makes experimental characterization of every target impractical.

The role of electrical and jasmonate signalling in the recognition of captured prey in the carnivorous sundew plant Drosera capensis

The carnivorous sundew plant (Drosera capensis) captures prey using sticky tentacles. We investigated the tentacle and trap reactions in response to the electrical and jasmonate signalling evoked by different stimuli to reveal how carnivorous sundews recognize digestible captured prey in their traps. We measured the electrical signals, phytohormone concentration, enzyme activities and Chla fluorescence in response to mechanical stimulation, wounding or insect feeding in local and systemic traps. Seven new proteins in the digestive fluid were identified using mass spectrometry. Mechanical stimuli and live prey induced a fast, localized tentacle-bending reaction and enzyme secretion at the place of application. By contrast, repeated wounding induced a nonlocalized convulsive tentacle movement and enzyme secretion in local but also in distant systemic traps. These differences can be explained in terms of the electrical signal propagation and jasmonate accumulation, which also had a significant impact on the photosynthesis in the traps. The electrical signals generated in response to wounding could partially mimic a mechanical stimulation of struggling prey and might trigger a false alarm, confirming that the botanical carnivory and plant defence mechanisms are related. To trigger the full enzyme activity, the traps must detect chemical stimuli from the captured prey.

Sequence comparison, molecular modeling, and network analysis predict structural diversity in cysteine proteases from the Cape sundew, Drosera capensis

Carnivorous plants represent a so far underexploited reservoir of novel proteases with potentially useful activities. Here we investigate 44 cysteine proteases from the Cape sundew, Drosera capensis, predicted from genomic DNA sequences. D. capensis has a large number of cysteine protease genes; analysis of their sequences reveals homologs of known plant proteases, some of which are predicted to have novel properties. Many functionally significant sequence and structural features are observed, including targeting signals and occluding loops. Several of the proteases contain a new type of granulin domain. Although active site residues are conserved, the sequence identity of these proteases to known proteins is moderate to low; therefore, comparative modeling with all-atom refinement and subsequent atomistic MD-simulation is used to predict their 3D structures. The structure prediction data, as well as analysis of protein structure networks, suggest multifarious variations on the papain-like cysteine protease structural theme. This in silico methodology provides a general framework for investigating a large pool of sequences that are potentially useful for biotechnology applications, enabling informed choices about which proteins to investigate in the laboratory.

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44 new cysteine proteases from the carnivorous plant Drosera capensis are described.

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Structure prediction and molecular dynamics simulation predict overall folds similar to papain.

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Functionally significant sequence and structural features are observed, including targeting signals and occluding loops.

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Several of the proteases contain a new type of granulin domain.

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Protein structure networks reveal global differences in interactions among chemical groups.