@article {4767, title = {An Antarctic alga that can survive the extreme cold}, journal = {Frontiers for Young Minds}, volume = {10}, year = {2022}, month = {05/2022}, pages = {740838}, abstract = {

Microscopic algae are tougher than you might think. Some can even survive the extreme cold. In this article, we describe one of the coolest algae of all, the Antarctic green alga called Chlamydomonas sp. UWO241. This one-celled super-organism lives deep in the frigid waters of a remote and permanently ice-covered lake in Antarctica. How does this little alga thrive in such a barren and unwelcoming place? Well, dive into this article to learn how studying the genome of UWO241 is helping scientists better understand this amazingly hardy alga.

}, keywords = {LTER-MCM}, doi = {10.3389/frym.2022.740838}, url = {https://kids.frontiersin.org/articles/10.3389/frym.2022.740838}, author = {Smith, David R. and Leung, Arthur and Zhang, Xi and Cvetkovska, Marina and Rachael M. Morgan-Kiss and H{\"u}ner, Norman P. A.} } @article {4766, title = {Cyclic electron flow (CEF) and ascorbate pathway activity provide constitutive photoprotection for the photopsychrophile, Chlamydomonas sp. UWO 241~(renamed Chlamydomonas priscuii)}, journal = {Photosynthesis Research}, volume = {151}, year = {2022}, month = {03/2022}, pages = {235 - 250}, abstract = {

Under environmental stress, plants and algae employ a variety of strategies to protect the photosynthetic apparatus and maintain photostasis. To date, most studies on stress acclimation have focused on model organisms which possess limited to no tolerance to stressful extremes. We studied the ability of the Antarctic alga Chlamydomonas sp. UWO 241 (UWO 241) to acclimate to low temperature, high salinity or high light. UWO 241 maintained robust growth and photosynthetic activity at levels of temperature (2 \°C) and salinity (700 mM NaCl) which were nonpermissive for a mesophilic sister species, Chlamydomonas raudensis SAG 49.72 (SAG 49.72). Acclimation in the mesophile involved classic mechanisms, including downregulation of light harvesting and shifts in excitation energy between photosystem I and II. In contrast, UWO 241 exhibited high rates of PSI-driven cyclic electron flow (CEF) and a larger capacity for nonphotochemical quenching (NPQ). Furthermore, UWO 241 exhibited constitutively high activity of two key ascorbate cycle enzymes, ascorbate peroxidase and glutathione reductase and maintained a large ascorbate pool. These results matched the ability of the psychrophile to maintain low ROS under short-term photoinhibition conditions. We conclude that tight control over photostasis and ROS levels are essential for photosynthetic life to flourish in a native habitat of permanent photooxidative stress. We propose to rename this organism Chlamydomonas priscuii.

}, keywords = {LTER-MCM, Antarctica, ascorbate, Cyclic electron flow, Photosystem I, Psychrophile, ROS}, doi = {10.1007/s11120-021-00877-5}, url = {https://link.springer.com/article/10.1007/s11120-021-00877-5}, author = {Stahl-Rommel, Sarah and Kalra, Isha and D{\textquoteright}Silva, Susanna and Hahn, Mark M. and Popson, Devon and Cvetkovska, Marina and Rachael M. Morgan-Kiss} } @article {4716, title = {Photosynthetic adaptation to polar life: Energy balance, photoprotection and genetic redundancy}, journal = {Journal of Plant Physiology}, volume = {268}, year = {2022}, month = {01/2022}, pages = {153557}, abstract = {

The persistent low temperature that characterize polar habitats combined with the requirement for light for all photoautotrophs creates a conundrum. The absorption of too much light at low temperature can cause an energy imbalance that decreases photosynthetic performance that has a negative impact on growth and can affect long-term survival. The goal of this review is to survey the mechanism(s) by which polar photoautotrophs maintain cellular energy balance, that is, photostasis to overcome the potential for cellular energy imbalance in their low temperature environments. Photopsychrophiles are photosynthetic organisms that are obligately adapted to low temperature (0-15 \°C) but usually die at higher temperatures (\≥20 \°C). In contrast, photopsychrotolerant species can usually tolerate and survive a broad range of temperatures (5-40 \°C). First, we summarize the basic concepts of excess excitation energy, energy balance, photoprotection and photostasis and their importance to survival in polar habitats. Second, we compare the photoprotective mechanisms that underlie photostasis and survival in aquatic cyanobacteria and green algae as well as terrestrial Antarctic and Arctic plants. We show that polar photopsychrophilic and photopsychrotolerant organisms attain energy balance at low temperature either through a regulated reduction in the efficiency of light absorption or through enhanced capacity to consume photosynthetic electrons by the induction of O2\ as an alternative electron acceptor. Finally, we compare the published genomes of three photopsychrophilic and one photopsychrotolerant alga with five mesophilic green algae including the model green alga, Chlamydomonas reinhardtii. We relate our genomic analyses to photoprotective mechanisms that contribute to the potential attainment of photostasis. Finally, we discuss how the observed genomic redundancy in photopsychrophilic genomes may confer energy balance, photoprotection and resilience to their harsh polar environment. Primary production in aquatic, Antarctic and Arctic environments is dependent on diverse algal and cyanobacterial communities. Although mosses and lichens dominate the Antarctic terrestrial landscape, only two extant angiosperms exist in the Antarctic. The identification of a single \‘molecular key\’ to unravel adaptation of photopsychrophily and photopsychrotolerance remains elusive. Since these photoautotrophs represent excellent biomarkers to assess the impact of global warming on polar ecosystems, increased study of these polar photoautotrophs remains essential.

}, keywords = {LTER-MCM, genomic redundancy, light, photoprotection, photopsychrophily, photopsychrotolerance, Photosynthesis, temperature}, doi = {10.1016/j.jplph.2021.153557}, url = {https://www.sciencedirect.com/science/article/pii/S0176161721001966}, author = {H{\"u}ner, Norman P. A. and Smith, David R. and Cvetkovska, Marina and Zhang, Xi and Alexander G. Ivanov and Szyszka-Mroz, Beth and Kalra, Isha and Rachael M. Morgan-Kiss} } @article {4634, title = {Draft genome sequence of the Antarctic green alga Chlamydomonas sp. UWO241}, journal = {iScience}, volume = {24}, year = {2021}, month = {2021-02}, pages = {102084}, abstract = {

Antarctica is home to an assortment of psychrophilic algae, which have evolved various survival strategies for coping with their frigid environments. Here, we explore Antarctic psychrophily by examining the \∼212 Mb draft nuclear genome of the green alga Chlamydomonas\ sp. UWO241, which resides within the water column of a perennially ice-covered, hypersaline lake. Like certain other Antarctic algae, UWO241 encodes a large number (\≥37) of ice-binding proteins, putatively originating from horizontal gene transfer. Even more striking, UWO241 harbors hundreds of highly similar duplicated genes involved in diverse cellular processes, some of which we argue are aiding its survival in the Antarctic via gene dosage. Gene and partial gene duplication appear to be an ongoing phenomenon within UWO241, one which might be mediated by retrotransposons. Ultimately, we consider how such a process could be associated with adaptation to extreme environments but explore potential non-adaptive hypotheses as well.

}, keywords = {LTER-MCM}, issn = {25890042}, doi = {10.1016/j.isci.2021.102084}, url = {https://www.sciencedirect.com/science/article/pii/S2589004221000523}, author = {Zhang, Xi and Cvetkovska, Marina and Rachael M. Morgan-Kiss and H{\"u}ner, Norman P. A. and Smith, David Roy} } @article {4419, title = {Chlamydomonas sp. UWO 241 exhibits high cyclic electron flow and rewired metabolism under high salinity}, journal = {Plant Physiology}, year = {2020}, month = {03/2020}, abstract = {

The Antarctic green alga Chlamydomonas sp. UWO 241 (UWO 241) is adapted to permanent low temperatures, hypersalinity, and extreme shade. one of the most striking phenotypes of UWO 241 is an altered photosystem I (PSI) organization and constitutive PSI cyclic electron flow (CEF). To date, little attention has been paid to CEF during long-term stress acclimation, and the consequences of sustained CEF in UWO 241 are not known. In this study, we combined photobiology, proteomics, and metabolomics to understand the underlying role of sustained CEF in high salinity stress acclimation. High salt-grown UWO 241 exhibited increased thylakoid proton motive flux and an increased capacity for non-photochemical quenching. Under high salt, a significant proportion of the upregulated enzymes were associated with the Calvin Benson Bassham Cycle, carbon storage metabolism, and protein translation. Two key enzymes of the Shikimate pathway, DAHP synthase and chorismate synthase, were also upregulated, as well as indole-3-glycerol phosphate synthase, an enzyme involved in the biosynthesis of L-tryptophan and indole acetic acid. In addition, several compatible solutes (glycerol, proline, and sucrose) accumulated to high levels in high salt-grown UWO 241 cultures. We suggest that UWO 241 maintains constitutively high CEF through the associated PSI-cytochrome b6f supercomplex to support robust growth and strong photosynthetic capacity under a constant growth regime of low temperatures and high salinity.

}, keywords = {LTER-MCM}, doi = {10.1104/pp.19.01280}, url = {http://www.plantphysiol.org/content/early/2020/04/03/pp.19.01280}, author = {Kalra, Isha and Wang, Xin and Cvetkovska, Marina and Jeong, Jooyeon and McHargue, William and Zhang, Ru and H{\"u}ner, Norman and Yuan, Joshua S. and Rachael M. Morgan-Kiss} }