Background Trichomonas vaginalis is a human-infecting trichomonad and as such the best studied and the only for which the full genome sequence is available considering its parasitic lifestyle, T. vaginalis encodes an unusually high number of proteins. Many gene families are massively expanded and some genes are speculated to have been acquired from prokaryotic sources. Among the latter are two gene families that harbour domains which share similarity with proteins of Bacteroidales/Spirochaetales and Chlamydiales: the BspA and the Pmp proteins, respectively. Results We sequenced the transcriptomes of five trichomonad species and screened for the presence of BspA and Pmp domain-containing proteins and characterized individual candidate proteins from both families in T. vaginalis . Here, we demonstrate that (i) BspA and Pmp domain-containing proteins are universal to trichomonads, but specifically expanded in T. vaginalis ; (ii) in line with a concurrent expansion of the endocytic machinery, there is a high number of BspA and Pmp proteins which carry C-terminal endocytic motifs; and (iii) both families traffic through the ER and have the ability to increase adhesion performance in a non-virulent T. vaginalis strain and Tetratrichomonas gallinarum by a so far unknown mechanism. Conclusions Our results initiate the functional characterization of these two broadly distributed protein families and help to better understand the origin and evolution of BspA and Pmp domains in trichomonads. Electronic supplementary material The online version of this article (10.1186/s13071-019-3660-z) contains supplementary material, which is available to authorized users.

Pyruvate : ferredoxin oxidoreductase (PFO) and iron only hydrogenase ([Fe]-HYD) are common enzymes among eukaryotic microbes that inhabit anaerobic niches. Their function is to maintain redox balance by donating electrons from food oxidation via ferredoxin (Fd) to protons, generating H 2 as a waste product. Operating in series, they constitute a soluble electron transport chain of one-electron transfers between FeS clusters. They fulfil the same function—redox balance—served by two electron-transfers in the NADH- and O 2 -dependent respiratory chains of mitochondria. Although they possess O 2 -sensitive FeS clusters, PFO, Fd and [Fe]-HYD are also present among numerous algae that produce O 2 . The evolutionary persistence of these enzymes among eukaryotic aerobes is traditionally explained as adaptation to facultative anaerobic growth. Here, we show that algae express enzymes of anaerobic energy metabolism at ambient O 2 levels (21% v/v), Chlamydomonas reinhardtii expresses them with diurnal regulation. High O 2 environments arose on Earth only approximately 450 million years ago. Gene presence/absence and gene expression data indicate that during the transition to high O 2 environments and terrestrialization, diverse algal lineages retained enzymes of Fd-dependent one-electron-based redox balance, while the land plant and land animal lineages underwent irreversible specialization to redox balance involving the O 2 -insensitive two-electron carrier NADH.

Summary To obtain insights into the dynamics of nutrient exchange in arbuscular mycorrhizal ( AM ) symbiosis, we modelled mathematically the two‐membrane system at the plant–fungus interface and simulated its dynamics. In computational cell biology experiments, the full range of nutrient transport pathways was tested for their ability to exchange phosphorus (P)/carbon (C)/nitrogen (N) sources. As a result, we obtained a thermodynamically justified, independent and comprehensive model of the dynamics of the nutrient exchange at the plant–fungus contact zone. The predicted optimal transporter network coincides with the transporter set independently confirmed in wet‐laboratory experiments previously, indicating that all essential transporter types have been discovered. The thermodynamic analyses suggest that phosphate is released from the fungus via proton‐coupled phosphate transporters rather than anion channels. Optimal transport pathways, such as cation channels or proton‐coupled symporters, shuttle nutrients together with a positive charge across the membranes. Only in exceptional cases does electroneutral transport via diffusion facilitators appear to be plausible. The thermodynamic models presented here can be generalized and adapted to other forms of mycorrhiza and open the door for future studies combining wet‐laboratory experiments with computational simulations to obtain a deeper understanding of the investigated phenomena.

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Elysia chlorotica is a kleptoplastic sea slug that preys on Vaucheria litorea, stealing its plastids which continue to photosynthesize for months inside the animal cells. We investigated the native properties of V. litorea plastids to understand how they withstand the rigors of photosynthesis in isolation. Transcription of specific genes in laboratory-isolated V. litorea plastids was monitored up to seven days. The involvement of plastid-encoded FtsH, a key plastid maintenance protease, in recovery from photoinhibition in V. litorea was estimated in cycloheximide-treated cells. In vitro comparison of V. litorea and spinach thylakoids was applied to investigate ROS formation in V. litorea. In comparison to other tested genes, the transcripts of ftsH and translation elongation factor EF-Tu (tufA) decreased slowly during incubation of isolated V. litorea plastids. Higher level of FtsH was also evident in cycloheximide-treated cells during recovery from photoinhibition. Charge recombination in PSII of V. litorea was found to be fine-tuned to produce only small quantities of singlet oxygen ( 1O2), and the plastids also contain ROS-protective compounds. Our results support the view that the genetic characteristics of the plastids themselves are crucial in creating a photosynthetic sea slug. The plastid’s autonomous repair machinery is likely enhanced by low 1O2 production and by elevated expression of FtsH in the plastids.

Elysia chlorotica is a kleptoplastic sea slug that preys on Vaucheria litorea, stealing its plastids which then continue to photosynthesize for months inside the animal cells. We investigated the native properties of V. litorea plastids to understand how they withstand the rigors of photosynthesis in isolation. Transcription of specific genes in laboratory-isolated V. litorea plastids was monitored up to seven days. The involvement of plastid-encoded FtsH, a key plastid maintenance protease, in recovery from photoinhibition in V. litorea was estimated in cycloheximide-treated cells. In vitro comparison of V. litorea and spinach thylakoids was applied to investigate ROS formation in V. litorea. Isolating V. litorea plastids triggered upregulation of ftsH and translation elongation factor EF-Tu (tufA). Upregulation of FtsH was also evident in cycloheximide-treated cells during recovery from photoinhibition. Charge recombination in PSII of V. litorea was found to be fine-tuned to produce only small quantities of singlet oxygen (1O2). Our results support the view that the genetic characteristics of the plastids themselves are crucial in creating a photosynthetic sea slug. The plastid's autonomous repair machinery is likely enhanced by low 1O2 production and by upregulation of FtsH in the plastids.

10While core components of plastid protein import (Toc and Tic) and the principle of using N-11 terminal targeting sequences (NTS) are conserved, lineage-specific differences are known. 12Rhodophytes and glaucophytes carry a conserved NTS motif, which was lost in the green 13 lineage that also added novel proteins to Toc and Tic. Here we compare the components of 14 plastid protein import and generated RNA-Seq, pigment profile and trans-electron microscopy 15data based on high-light stress from representatives of the three archaeplastidal groups. In light 16 of plastid protein targeting, we compare the response to high-light stress of archaeplastidal 17representatives based on RNA-Seq, pigment profile and trans-electron microscopy data. Like 18 land plants, the chlorophyte Chlamydomonas reinhardtii displays a broad respond to high-light 19 stress, not observed to the same degree in the glaucophyte Cyanophora paradoxa or the 20 rhodophyte Porphyridium purpureum. We find that only the green lineage encodes a conserved 21 duplicate of the outer plastid membrane protein channel Oep80, namely Toc75 and suggest that 22 the ability to respond to high-light stress entailed evolutionary changes in protein import, 23including the departure from phenylalanine-based targeting and the introduction of a green-24 specific Toc75 next to other import components unique to Chloroplastida. One consequence of 25 relaxed NTS specificity was the origin of dual-targeting of plastid derived proteins to 26 mitochondria and vice versa, using a single ambiguous NTS. Changes in the plastid protein 27 import enabled the green lineage to import proteins at a more efficient rate, including those 28 required for high-light stress response, a prerequisite for the colonization of land. 29 30

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