Abstract
Carnivorous pitcher plants produce specialised pitcher organs containing secretory glands, which secrete acidic fluids with hydrolytic enzymes for prey digestion and nutrient absorption. The content of pitcher fluids has been the focus of many fluid protein profiling studies. These studies suggest an evolutionary convergence of a conserved group of similar enzymes in diverse families of pitcher plants. A recent study showed that endogenous proteins were replenished in the pitcher fluid, which indicates a feedback mechanism in protein secretion. This poses an interesting question on the physiological effect of plant protein loss. However, there is no study to date that describes the pitcher response to endogenous protein depletion. To address this gap of knowledge, we previously performed a comparative RNA-sequencing experiment of newly opened pitchers (D0) against pitchers after 3 days of opening (D3C) and pitchers with filtered endogenous proteins (>10 kDa) upon pitcher opening (D3L). Nepenthes ampullaria was chosen as a model study species due to their abundance and unique feeding behaviour on leaf litters. The analysis of unigenes with top 1% abundance found protein translation and stress response to be overrepresented in D0, compared to cell wall related, transport, and signalling for D3L. Differentially expressed gene (DEG) analysis identified DEGs with functional enrichment in protein regulation, secondary metabolism, intracellular trafficking, secretion, and vesicular transport. The transcriptomic landscape of the pitcher dramatically shifted towards intracellular transport and defence response at the expense of energy metabolism and photosynthesis upon endogenous protein depletion. This is supported by secretome, transportome, and transcription factor analysis with RT-qPCR validation based on independent samples. This study provides the first glimpse into the molecular responses of pitchers to protein loss with implications to future cost/benefit analysis of carnivorous pitcher plant energetics and resource allocation for adaptation in stochastic environments.
Highlights
Carnivorous plants are commonly found in habitats deprived of nutrients, especially nitrogen and phosphorus
34,444 (21.7%) unigenes were annotated with gene ontology (GO) terms through BLAST and Pfam analyses, in which 27,646 unigenes categorised in cellular component, 28,839 unigenes in molecular function, and 26,926 unigenes in biological process (Fig. S1)
Based on previous reports on pitcher fluid protein profiling[2,15,16,37], we identified the homologous unigenes encoding secreted proteins, namely aspartic protease (Nep), neprosin (Npr), cysteine protease, serine carboxypeptidase (SCP), purple acid phosphatase (PAP), S-like ribonuclease (RNase), α-glucosidase, β-1,3-glucanase, galactosidase, endonuclease (Endo), GDSL esterase/lipase, peroxidase (Prx), chitinase (Chit), pathogenesis-related (PR) protein, thaumatin-like protein (TLP), and desiccation-related protein (DRP) (Fig. 5)
Summary
Carnivorous plants are commonly found in habitats deprived of nutrients, especially nitrogen and phosphorus. The findings that many proteases, chitinases, and glucanases found in the pitcher fluids can be classified as PR proteins led to the inference that offensive carnivory mechanism evolved from existing plant defensive mechanism against herbivory[22] This is supported by the conserved jasmonate signalling of enzyme secretion during prey capture[23,24]. The adaptive radiation of N acquisition in N. ampullaria through plant materials as well as insect prey by retaining a large slippery peristome in prey capture[33] and endochitinase activities in the pitcher fluid[34] explains its wide range of distribution and often co-exists with other insectivorous species[25]. What are the transcriptional regulatory factors responsive to the changes in pitcher fluid proteins?
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
