Biology subjects

Handrich, M.

Publications and source records attributed to Handrich, M..

3 recordsLinked to original sources

bioRxiv2021

Genetic autonomy and low singlet oxygen yield support kleptoplast functionality in photosynthetic sea slugs

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 plastids autonomous repair machinery is likely enhanced by low 1O2 production and by upregulation of FtsH in the plastids. HighlightIsolated Vaucheria litorea plastids exhibit upregulation of tufA and ftsH, key plastid maintenance genes, and produce only little singlet oxygen. These factors likely contribute to plastid longevity in kleptoplastic slugs.

plant biology↗

bioRxiv2019

Major changes in plastid protein import and the origin of the Chloroplastida

While core components of plastid protein import (Toc and Tic) and the principle of using N-terminal targeting sequences (NTS) are conserved, lineage-specific differences are known. Rhodophytes and glaucophytes carry a conserved NTS motif, which was lost in the green lineage that also added novel proteins to Toc and Tic. Here we compare the components of plastid protein import and generated RNA-Seq, pigment profile and trans-electron microscopy data based on high-light stress from representatives of the three archaeplastidal groups. In light of plastid protein targeting, we compare the response to high-light stress of archaeplastidal representatives based on RNA-Seq, pigment profile and trans-electron microscopy data. Like land plants, the chlorophyte Chlamydomonas reinhardtii displays a broad respond to high-light stress, not observed to the same degree in the glaucophyte Cyanophora paradoxa or the rhodophyte Porphyridium purpureum. We find that only the green lineage encodes a conserved duplicate of the outer plastid membrane protein channel Oep80, namely Toc75 and suggest that the ability to respond to high-light stress entailed evolutionary changes in protein import, including the departure from phenylalanine-based targeting and the introduction of a green-specific Toc75 next to other import components unique to Chloroplastida. One consequence of relaxed NTS specificity was the origin of dual-targeting of plastid derived proteins to mitochondria and vice versa, using a single ambiguous NTS. Changes in the plastid protein import enabled the green lineage to import proteins at a more efficient rate, including those required for high-light stress response, a prerequisite for the colonization of land.\n\nHigh-lightsO_LILoss of Phe-based N-terminal targeting sequences (NTS) triggered the origin of dual-targeting using a single ambiguous NTS\nC_LIO_LIThe Chloroplastida evolved a green-specific Toc75 for high throughput import, next to a universal and ancient Omp85 present in all Archaeplastida\nC_LIO_LIA broad response to high-light stress appears unique to Chloroplastida\nC_LIO_LIRelaxation of functional constraints allowed a broader modification of the green Toc/Tic machinery\nC_LIO_LICritical changes in plastid targeting enabled the origin and success of the Chloroplastida and their later conquer of land\nC_LI

evolutionary biology↗

bioRxiv2019

Adaptation to life on land at 21% O2 via transition from ferredoxin- to NADH-dependent redox balance

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 H2 as a waste product. Operating in series, they constitute a soluble electron transport chain of one-electron transfers between FeS clusters. They fulfill the same function -- redox balance -- served by two electron-transfers in the NADH- and O2-dependent respiratory chains of mitochondria. Although they possess O2-sensitive FeS clusters, PFO, Fd and [Fe]-HYD are also present among numerous algae that produce O2. The evolutionary persistence of these enzymes among eukaryotic aerobes is traditionally explained as enabling facultative anaerobic growth. Here we show that algae express enzymes of anaerobic energy metabolism at ambient O2 levels (21% v/v), Chlamydomonas reinhardtii expresses them with diurnal regulation. High O2 environments arose on Earth only some [~]450 million years ago. Gene presence absence and gene expression data indicate that during the transition to high O2 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 O2-insensitive two-electron carrier NADH.\n\nHighlights- Algae express enzymes of anaerobic metabolism in 21% [v/v] O2 atmosphere, independent of anaerobiosis\n- Retention of a plastid-encoded NADH dehydrogenase-like (NDH) was likely a prerequisite for the transition to life on land\n- Terrestrialization and adaption to high O2 is accompanied by a shift to redox balance at higher midpoint potentials\n- Eukaryotes adapted to high O2 life on land via specialization to two-electron based redox balance

evolutionary biology↗