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

Abstract

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.

Transcriptome-wide shift from photosynthesis and energy metabolism upon endogenous fluid protein depletion in young Nepenthes ampullaria pitchers

“…5) already showed high expression levels on D0. This corroborates findings that most of the endogenous secreted proteins already present in pitcher fluids before opening with certain proteins continuously replenished or induced by prey 15,34,37,46 . In comparison, there was no clear trend in the expression of transporters on D0 (Fig.…”

“…The pitchers can detect enzymes in the pitcher fluids and respond accordingly to maintain an optimal cocktail of enzymes so that the benefits from prey digestion outweigh the costs of protein replenishment and pitcher metabolisms. Other studies also revealed that pitchers can regulate enzyme activities 24,46,58 . This is likely involving Ca 2+ and jasmonic acid (JA) signal transduction pathways 22 .…”

“…In Drosera rotundifolia, both chitin and protein applications enhanced chitinase and Scientific RepoRtS | (2020) 10:6575 | https://doi.org/10.1038/s41598-020-63696-z www.nature.com/scientificreports www.nature.com/scientificreports/ protease activities 59 . Contrasting chitin, proteins seem to be much better inductors of various enzymes, such as phosphatases, proteases, and chitinases, in pitchers of Nepenthes 46 and Sarracenia 60 . Proteins mimic the insect prey best and activate the highest expression of cysteine protease and type I chitinase in Venus flytrap 61 .…”

“…5). It is surprising to find a prey-induced chitinase gene 46 to be upregulated by protein loss. Chitinases are antifungal and degrade insect cuticle, in which class IV endochitinases hydrolyse shorter chitin chains derived from the products of class III endochitinases from longer chitin polymers 16,51 .…”

Investigation of an Elevational Gradient Reveals Strong Differences Between Bacterial and Eukaryotic Communities Coinhabiting Nepenthes Phytotelmata

“…This suggests that all four culicid morphospecies are equally tolerant of acidic conditions, rather than the existence of multiple species with different physiological tolerances that only co-occur in more moderate conditions. Prey capture induces fluid acidification [100,101], and an increase in nutrient availability could explain the relationship between high abundance of ants, other insect prey, and mites with low pH.…”