A Constitutive Stress Response is an Adaptation to Low Temperature in
the Antarctic green alga Chlamydomonas sp. UWO241
Abstract
The Antarctic green alga Chlamydomonas sp. UWO241 is an obligate
psychrophile that thrives in the cold (4-6°C) but is unable to survive
at temperatures ≥18°C. Little is known how exposure to heat affects its
physiology or whether it mounts a heat stress response in a manner
comparable to mesophiles. Here, we dissect the responses of UWO241 to
temperature stress by examining its growth, primary metabolome and
transcriptome under steady-state low temperature and heat stress
conditions. In comparison with Chlamydomonas reinhardtii, UWO241
constitutively accumulates metabolites and proteins commonly considered
as stress markers, including soluble sugars, antioxidants, polyamines,
and heat shock proteins to ensure efficient protein folding at low
temperatures. We propose that this permanent stress metabolism is an
adaptive advantage to life at extreme conditions. A shift from 4°C to a
non-permissive temperature of 24°C alters the UWO241 primary metabolome
and transcriptome, but growth of UWO241 at higher permissive
temperatures (10°C and 15°C) does not provide enhanced heat protection.
UWO241 also fails to induce the accumulation of HSPs when exposed to
heat, suggesting that it has lost the ability to fine-tune its heat
stress response. Our work adds to the growing body of research on
temperature stress in psychrophiles, many of which are threatened by
climate change.