Biology subjects

Tyystjärvi, E.

Publications and source records attributed to Tyystjärvi, E..

5 recordsLinked to original sources

bioRxiv2024

Evolution and theft: loss of state transitions in Bryopsidales macroalgae and photosynthetic sea slugs

Green macroalgae within the order Bryopsidales lack the fundamental photoprotective mechanisms of green algae, the xanthophyll cycle and energy-dependent dissipation of excess light. Here, by measuring chlorophyll fluorescence at 77K after specific light treatments, we show that Bryopsidales algae also lack state transitions, another ubiquitous photoprotection mechanism present in other green algae. Certain Sacoglossa sea slugs can feed on Ulvophyceae algae, including some Bryopsidales, and steal chloroplasts -kleptoplasts- that remain functional inside the animal cells for months without the support of the algal nucleus. Our data reveal that the state transition capacity is not retained in the kleptoplasts of the sea slugs, and we provide evidence that the loss is caused by structural changes during their incorporation by the animals. This enforced chloroplast sphericity was observed in all studied kleptoplastic associations, and we propose that it is a fundamental property supporting long-term retention of kleptoplasts in photosynthetic sea slugs.

plant biology↗

bioRxiv2021

Ultraviolet screening by slug tissue and tight packing of plastids protect photosynthetic sea slugs from photoinhibition

O_LIOne of the main unsolved questions regarding photosynthetic sea slugs is how the slug plastids handle photoinhibition of Photosystem II. Photoinhibition has not been studied in detail in these animals although resilience against photoinhibition might obviously explain the longevity of plastids inside animal cytosol. C_LIO_LILight response and action spectrum of photoinhibition were measured from the slug Elysia timida and its prey alga Acetabularia acetabulum. Plastid packing in the slugs and algae was compared with spectroscopic and microscopic methods. The importance of plastid concentration was also estimated by measuring photoinhibition from starved slugs. C_LIO_LICompared to A. acetabulum, E. timida is highly resistant against photoinhibition. The resilience of the slugs is even more pronounced in the UV-region, as the slug tissue screens UV radiation. The plastids in the slug tissue are tightly packed, and the outer plastids protect the inner ones from photoinhibition. C_LIO_LIThe sea slug E. timida protects its plastids from photoinhibition by screening UV radiation and packing the plastids tightly in its tissues. Both mechanisms enhance the longevity of the plastids in slug cytosol and ameliorate the need for repair of photoinhibited Photosystem II. C_LI

plant biology↗

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↗

bioRxiv2020

Photosynthetic sea slugs inflict protective changes to the light reactions of the chloroplasts they steal from algae

Sacoglossan sea slugs are able to maintain functional chloroplasts inside their own cells, and mechanisms that allow preservation of the chloroplasts are unknown. We found that the slug Elysia timida inflicts changes to the photosynthetic light reactions of the chloroplasts it steals from the alga Acetabularia acetabulum. Working with a large continuous laboratory culture of both the slugs (>500 individuals) and their prey algae, we show that the plastoquinone pool of slug chloroplasts remains oxidized, which can suppress reactive oxygen species formation. Slug chloroplasts also rapidly build up a strong proton motive force upon a dark-to-light transition, which helps them to rapidly switch on photoprotective non-photochemical quenching of excitation energy. Finally, our results suggest that chloroplasts inside E. timida rely on flavodiiron proteins as electron sinks during rapid changes in light intensity. These photoprotective mechanisms are expected to contribute to the long-term functionality of the chloroplasts inside the slugs.

cell biology↗

bioRxiv2018

RCD1 Coordinates Chloroplastic and Mitochondrial Electron Transfer through Interaction with ANAC Transcription Factors

Signaling from chloroplasts and mitochondria, both dependent on reactive oxygen species (ROS), merge at the nuclear protein RADICAL-INDUCED CELL DEATH1 (RCD1). ROS produced in the chloroplasts affect the abundance, thiol redox state and oligomerization of RCD1. RCD1 directly interacts in vivo with ANAC013 and ANAC017 transcription factors, which are the mediators of the ROS-related mitochondrial complex III retrograde signa and suppresses activity of ANAC013 and ANAC017. Inactivation of RCD1 leads to increased expression of ANAC013 and ANAC017-regulated genes belonging to the mitochondrial dysfunction stimulon (MDS), including genes for mitochondrial alternative oxidases (AOXs). Accumulating AOXs and other MDS gene products alter electron transfer pathways in the chloroplasts, leading to diminished production of chloroplastic ROS and increased protection of photosynthetic apparatus from ROS damage. RCD1-dependent regulation affects chloroplastic and mitochondrial retrograde signaling including chloroplast signaling by 3-phosphoadenosine 5-phosphate (PAP). Sensitivity of RCD1 to organellar ROS provides feedback control of nuclear gene expression.

plant biology↗