02098nas a2200265 4500008004100000022001400041245010400055210006900159260001200228300001200240490000800252520131200260653001601572653001501588653001801603653002501621653002101646653001301667653002201680100001601702700001401718700001401732700002901746856005701775 2023 eng d a0166-859500aHigh salt-induced PSI-supercomplex is associated with high CEF and attenuation of state transitions0 aHigh saltinduced PSIsupercomplex is associated with high CEF and c09/2023 a65 - 840 v1573 a

While PSI-driven cyclic electron flow (CEF) and assembly of thylakoid supercomplexes have been described in model organisms like Chlamydomonas reinhardtii, open questions remain regarding their contributions to survival under long-term stress. The Antarctic halophyte, C. priscuii UWO241 (UWO241), possesses constitutive high CEF rates and a stable PSI-supercomplex as a consequence of adaptation to permanent low temperatures and high salinity. To understand whether CEF represents a broader acclimation strategy to short- and long-term stress, we compared high salt acclimation between the halotolerant UWO241, the salt-sensitive model, C. reinhardtii, and a moderately halotolerant Antarctic green alga, C. sp. ICE-MDV (ICE-MDV). CEF was activated under high salt and associated with increased non-photochemical quenching in all three Chlamydomonas species. Furthermore, high salt-acclimated cells of either strain formed a PSI-supercomplex, while state transition capacity was attenuated. How the CEF-associated PSI-supercomplex interferes with state transition response is not yet known. We present a model for interaction between PSI-supercomplex formation, state transitions, and the important role of CEF for survival during long-term exposure to high salt.

10aacclimation10aAntarctica10aChlamydomonas10aCyclic electron flow10aPSI-supercomplex10asalinity10astate transitions1 aKalra, Isha1 aWang, Xin1 aZhang, Ru1 aMorgan-Kiss, Rachael, M. uhttps://link.springer.com/10.1007/s11120-023-01032-y02207nas a2200205 4500008004100000245010800041210006900149260001200218520152500230100001601755700001401771700002301785700001901808700002201827700001401849700001901863700002101882700002901903856006901932 2020 eng d00aChlamydomonas sp. UWO 241 exhibits high cyclic electron flow and rewired metabolism under high salinity0 aChlamydomonas sp UWO 241 exhibits high cyclic electron flow and  c03/20203 a

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.

1 aKalra, Isha1 aWang, Xin1 aCvetkovska, Marina1 aJeong, Jooyeon1 aMcHargue, William1 aZhang, Ru1 aHüner, Norman1 aYuan, Joshua, S.1 aMorgan-Kiss, Rachael, M. uhttp://www.plantphysiol.org/content/early/2020/04/03/pp.19.0128002684nas a2200265 4500008004100000022001400041245014900055210006900204260001200273490000600285520185300291653001502144653002502159653000902184653001802193653001702211100001502228700001802243700001602261700001202277700001402289700002102303700002902324856006502353 2019 eng d a0166-859500aThe Antarctic psychrophiles Chlamydomonas spp. UWO241 and ICE-MDV exhibit differential restructuring of photosystem I in response to iron0 aAntarctic psychrophiles iChlamydomonasi spp UWO241 and ICEMDV ex c02/20190 v93 a

Chlamydomonas sp. UWO241 is a psychrophilic alga isolated from the deep photic zone of a perennially ice-covered Antarctic lake (east lobe Lake Bonney, ELB). Past studies have shown that C. sp. UWO241 exhibits constitutive downregulation of photosystem I (PSI) and high rates of PSI-associated cyclic electron flow (CEF). Iron levels in ELB are in the nanomolar range leading us to hypothesize that the unusual PSI phenotype of C. sp. UWO241 could be a response to chronic Fe-deficiency. We studied the impact of Fe availability in C. sp. UWO241, a mesophile, C. reinhardtii SAG11-32c, as well as a psychrophile isolated from the shallow photic zone of ELB, Chlamydomonas sp. ICE-MDV. Under Fe-deficiency, PsaA abundance and levels of photooxidizable P700 (ΔA820/A820) were reduced in both psychrophiles relative to the mesophile. Upon increasing Fe, C. sp. ICE-MDV and C. reinhardtii exhibited restoration of PSI function, while C. sp. UWO241 exhibited only moderate changes in PSI activity and lacked almost all LHCI proteins. Relative to Fe-excess conditions (200 μM Fe2+), C. sp. UWO241 grown in 18 μM Fe2+ exhibited downregulation of light harvesting and photosystem core proteins, as well as upregulation of a bestrophin-like anion channel protein and two CEF-associated proteins (NdsS, PGL1). Key enzymes of starch synthesis and shikimate biosynthesis were also upregulated. We conclude that in response to variable Fe availability, the psychrophile C. sp. UWO241 exhibits physiological plasticity which includes restructuring of the photo-chemical apparatus, increased PSI-associated CEF, and shifts in downstream carbon metabolism toward storage carbon and secondary stress metabolites.

10aAntarctica10aCyclic electron flow10aIron10aPhotosystem I10aPsychrophile1 aCook, Greg1 aTeufel, Amber1 aKalra, Isha1 aLi, Wei1 aWang, Xin1 aPriscu, John, C.1 aMorgan-Kiss, Rachael, M. uhttps://link.springer.com/article/10.1007/s11120-019-00621-0