Biology subjects

Kraemer, L.

Publications and source records attributed to Kraemer, L..

4 recordsLinked to original sources

bioRxiv2025

Past thermal history and heat stress shape patterns of coral-algal symbioses in massive Porites

Massive corals, like some Porites species, are key reef-builders and provide critical habitat on coral reefs. Porites often exhibit high tolerance to stressors, like warming from climate change, although the drivers of these patterns are unclear. Using high-throughput sequencing, we examined whether associations with Symbiodiniaceae underpin this tolerance. Symbiodiniaceae diversity and community composition within two massive species (Porites lutea and P. lobata), whose identities were verified through morphometric examinations, were examined across 200 km of Ningaloo World Heritage Reef, Australia. Contrary to previous studies showing low diversity of high-fidelity symbionts, we found significant variability within Cladocopium, which differed significantly across host species, reef sites, and temperature metrics. Locations with broader temperature ranges and a greater number of extreme accumulated heat stress events (measured as [≥] 8 Degree Heating Weeks) exhibited significantly higher prevalence and abundance of thermotolerant Cladocopium C116. Community structure also varied significantly by the number of DHW events per location, where a low level of disturbance (1-3 events) resulted in a relatively lower community diversity compared to sites with 3-6 and 6-9 events. The southernmost and coolest site (in terms of Maximum Monthly Mean) harboured the greatest Symbiodiniaceae community diversity, whereas the northernmost and warmest site harboured the greatest Symbiodiniaceae sequence diversity. These lines of evidence suggest that Porites may hold greater capacity to vary, and by extension modify, their symbiont community diversity than previously thought. This flexibility could contribute to the genus Porites long-term evolutionary success and relative resilience to global marine heatwaves.

ecology↗

bioRxiv2022

MitoStores: Chaperone-controlled protein granules store mitochondrial precursors in the cytosol

Hundreds of mitochondrial precursor proteins are synthesized in the cytosol and imported into mitochondria in a post-translational reaction. The early processes associated with mitochondrial protein targeting remain poorly understood. Here we show that in bakers yeast, the cytosol has the capacity to transiently store matrix-destined precursors in dedicated deposits which we named MitoStores. MitoStores are strongly enhanced when protein import into mitochondria is competitively inhibited by a clogging of mitochondrial import sites, but also formed under physiological conditions when cells grow on non-fermentable carbon sources. MitoStores are enriched for a specific subset of nuclear encoded mitochondrial proteins, in particular those containing N-terminal mitochondrial targeting sequences. MitoStore formation is controlled by the heat shock proteins Hsp42 and Hsp104, potentially to suppress the toxic potential of accumulating mitochondrial precursor proteins. Thus, the cytosolic protein quality control system plays an active role during early stages in mitochondrial protein targeting by the coordinated and localized sequestration of mitochondrial precursor proteins. SummaryThe yeast cytosol can deposit precursors of mitochondrial proteins in specific granules called MitoStores. MitoStores are controlled by the cytosolic chaperone system, in particular by Hsp42 and Hsp104. MitoStore formation suppresses the toxicity arising from non-imported mitochondrial precursor proteins.

biochemistry↗

bioRxiv2021

The unfolded protein response of the endoplasmic reticulum supports mitochondrial biogenesis by buffering non-imported proteins

Almost all mitochondrial proteins are synthesized in the cytosol and subsequently targeted to mitochondria. The accumulation of non-imported precursor proteins occurring upon mitochondrial dysfunction can challenge cellular protein homeostasis. Here we show that blocking protein translocation into mitochondria results in the accumulation of mitochondrial membrane proteins at the endoplasmic reticulum, thereby triggering the unfolded protein response (UPRER). Moreover, we find that mitochondrial membrane proteins are also routed to the ER under physiological conditions. The levels of ER-resident mitochondrial precursors is enhanced by import defects as well as metabolic stimuli that increase the expression of mitochondrial proteins. Under such conditions, the UPRER is crucial to maintain protein homeostasis and cellular fitness. We propose the ER serves as a physiological buffer zone for those mitochondrial precursors that cant be immediately imported into mitochondria while engaging the UPRER to adjust the ER proteostasis capacity to the extent of precursor accumulation.

cell biology↗

bioRxiv2020

The mitochondrial surface receptor Tom70 protects the cytosol against mitoprotein-induced stress

Most mitochondrial proteins are synthesized as precursors in the cytosol and post-translationally transported into mitochondria. The mitochondrial surface protein Tom70 acts at the interface of the cytosol and mitochondria. In vitro import experiments identified Tom70 as targeting receptor, particularly for hydrophobic carriers. Using in vivo methods and high content screens, we revisited the question of Tom70 function and considerably expanded the set of Tom70-dependent mitochondrial proteins. We demonstrate that the crucial activity of Tom70 is its ability to recruit cytosolic chaperones to the outer membrane. Indeed, tethering an unrelated chaperone-binding domain onto the mitochondrial surface complements most of the defects caused by Tom70 deletion. Tom70-mediated chaperone recruitment reduces the proteotoxicity of mitochondrial precursor proteins, in particular of hydrophobic inner membrane proteins. Thus, our work suggests that the predominant function of Tom70 is to tether cytosolic chaperones to the outer mitochondrial membrane, rather than to serve as a mitochondria-specifying targeting receptor.

cell biology↗