Thylakoid Phosphorylation And Cell Morphology In The Antarctic Psychrophile, Chlamydomonas sp. UWO241

The unicellular green microalga, Chlamydomonas sp. UWO 241, was isolated from Lake Bonney, Antarctica. A unique characteristic of this algal strain is its inability to undergo state transitions combined with an altered thylakoid protein phosphorylation profile, which suggests the absence of LHCII phosphorylation, and preferential phosphorylation of a set of novel proteins. Examination of the unique phosphoproteins revealed that they are associated with a large pigment-protein supercomplex, which contains components of both photosystem I and the cytochrome b6/f complex and likely functions in cyclic electron flow (CEF). The absence of phosphorylation of LHCII proteins, associated with state transitions, was also investigated in UWO241. Although it was demonstrated that the Stt7 kinase involved in state transitions is present in the Antarctic psychrophile, minimal phosphorylation of minor LHCII polypeptides occurred due to the absence of 5/7 phosphorylation sites of Lhcb4 and Lhcb5, believed to play key roles during the transition from state I to state II. Therefore, it appears that UWO241 favours phosphorylation of a PSI-Cyt b6/f supercomplex to regulatePSI CEF rather than regulation of state transitions through the phosphorylation of LHCII proteins. UWO241 exists either as flagellated, single cells, or as non-motile, multicellular “palmelloids”. Interestingly, UWO241 cultures grown at 11°C exhibited nearly homogenous populations of single cells, while growth at 16°C induced a high ratio of palmelloids to single cells. A cell filtration technique was established to separate these morphological structures, and demonstrated that single cells and palmelloids of UWO241 exhibit structural and functional differences in photosynthetic activity