Department of Microbiology, Miami University, 700 E High St., 32 Pearson Hall, Oxford, OH, 45056, USA.
Land Resources and Environmental Sciences, Montana State University, Bozeman, MT, USA.
Photosynth Res. 2019 Aug;141(2):209-228. doi: 10.1007/s11120-019-00621-0. Epub 2019 Feb 7.
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 (ΔA/A) 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 Fe), C. sp. UWO241 grown in 18 µM Fe 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 photochemical apparatus, increased PSI-associated CEF, and shifts in downstream carbon metabolism toward storage carbon and secondary stress metabolites.
衣藻 sp. UWO241 是一种嗜冷藻类，从常年冰封的南极湖（ELB 的东湖区）的透光带深处分离得到。过去的研究表明，衣藻 sp. UWO241 表现出组成型下调的光系统 I（PSI）和高 PSI 相关循环电子流（CEF）速率。ELB 中的铁含量处于纳摩尔范围内，这使我们假设衣藻 sp. UWO241 的不寻常 PSI 表型可能是对慢性缺铁的反应。我们研究了铁可用性对衣藻 sp. UWO241 的影响，衣藻 sp. UWO241 是一种中温生物，而 C. reinhardtii SAG11-32c 是一种嗜热生物，以及从 ELB 透光带浅层分离的一种嗜冷生物，衣藻 sp. ICE-MDV。在缺铁条件下，与中温生物相比，两种嗜冷生物的 PsaA 丰度和可光氧化 P700（ΔA/A）水平降低。当增加铁时，衣藻 sp. ICE-MDV 和 C. reinhardtii 表现出 PSI 功能的恢复，而衣藻 sp. UWO241 仅表现出 PSI 活性的适度变化，并且几乎没有所有的 LHCI 蛋白。与铁过量条件（200 μM Fe）相比，在 18 μM Fe 中生长的衣藻 sp. UWO241 表现出光捕获和光系统核心蛋白的下调，以及类 Bestrophin 阴离子通道蛋白和两种 CEF 相关蛋白（NdsS、PGL1）的上调。淀粉合成和莽草酸生物合成的关键酶也上调。我们得出结论，为了应对可变的铁可用性，嗜冷生物衣藻 sp. UWO241 表现出生理可塑性，包括光化学仪器的重构、PSI 相关 CEF 的增加，以及下游碳代谢向储存碳和次级应激代谢物的转移。
