Photosynthetic Stress Response in Antarctic Algae Chlamydomonas priscuii

Abstract:

The algae of the McMurdo Dry Valley (MDV) lakes in Antarctica present a unique opportunity to analyze the variety of responses to photosynthetic stress. These lakes are low in nutrients, perennially covered in ice, and exposed to varying light intensities throughout the year. As such, extremophilic organisms like Chlamydomonas priscui (isolated from Lake Bonney of the MDV Lakes) may offer alternative solutions to problems created in the photosynthetic apparatuses by fluctuations in light and salt levels as a result of global climate change. Here, we are interested in how these organisms alter gene expression to support survivability of the cell and keep their photosynthetic mechanisms running over a time continuum of stress. Analyzing the RNA will provide additional insight into which genes are  expressed, and how they vary at different light and salt levels over a long time period. Samples were collected from continuous cultures at several timepoints and cryopreserved. The continuous cultures were conducted in photobioreactors (FMT150, Photon Systems Instruments) and measurements were taken continuously, every few minutes, or days to verify stress levels in the algae. Once we have validated our RNA and cDNA procedures with practice samples, RNA will be extracted from the preserved samples, converting it to cDNA, then probed with qPCR targeting a suite of key photosynthetic and stress genes. We will also compare the results of C. priscui to Chlamydomonas reinhardtii, a similar mesophilic strain, so that we can understand how stress adaptation impacts the response to these environmental conditions. We hypothesize that expression of key photosynthetic genes will exhibit species-specific temporal patterns, paralleling results from photobiology measurements All the data related presents interesting insight regarding the responses that extremophilic organisms like C. priscui may take to increase their photosynthetic output and sustain their survivability despite significant environmental shifts due to climate change.

Introduction:

Due to global climate change effects, we are seeing a decrease or stagnation in crop years in recent years. This dilemma necessitates strategies that improve crops photosynthetic efficiency to continue to support a growing human population globally. Abiotic stress, such as high light and salt, is a major driver of photosynthetic losses and thus a deeper understanding of the variety of photosynthetic stress responses could be used to improve stress tolerance in critical crops. Extremophilic algae such as Chlamydomonas priscui, isolated from Lake Bonney in the McMurdo Dry Valleys, Antarctica, provide models to explore the impacts of stress adaptation on photoacclimation. Lake Bonney is characterized by low light due to the perennial ice cover, low nutrients, high salt, and low temperature. Previous studies of C. priscui in lab have indicated stress adaptation results in alternative strategies for photosynthetic stress response especially when compared to their mesophilic relatives Chlamydomonas reinhardtii. In a recent high light stress experiment, C. priscui was shown to recover photosynthetic function whereas C. reinhardtii exhibited a sustained reduction in photosynthetic activity. With this knowledge in mind, the next step is to figure out how these distinct responses are regulated by looking at photosynthetic, carbon metabolism, and oxidative stress related gene expression through the time continuum of stress acclimation.

Collection: 

• C. reinhardtii grown in photobioreactors

  • Continuous culture (fresh media, waste removal)

  • Stress administered once 

  • Consistent measurements on photosynthetic stress and efficiency

Analysis: 

• RNA Extraction:

  • Kit: Maxwell 16 LEV Plant RNA (Promega, AS1430)

  • Quality Analysis: Nanodrop and Bioanalyzer (Agilent RNA Pico kit)

• cDNA Synthesis:

  • Kit: AppliedBiosystems (Thermofisher Cat #43-874-06) High-Capacity RNA-to-cDNA

• qPCR:

  • Kit: Bioline SensiFAST Sybr No-ROX 

• Repeat this experiment with high salt/light samples for C. reinhardtii

• Repeat experiment with high light and salt for C. priscui and compare C. reinhardtii 

• Conduct transcriptomics

Kinnunen P, Heino M, Sandström V, Taka M, Ray DK, Kummu M. Crop

Yield Loss Risk Is Modulated by Anthropogenic Factors. Earth's

Future. 2022Sep;10(9):e2021EF002420. doi: 10.1029/2021EF002420. Epub 2022 Sep26. PMID: 36583138; PMCID: PMC9786645

Stahl-Rommel, S., Kalra, I., D’Silva, S. et al. Cyclic electron flow (CEF) 

and ascorbate pathway activity provide constitutive photoprotection

for thephotopsychrophile, Chlamydomonas sp. UWO 241 (renamed

Chlamydomonas priscuii). Photosynth Res 151, 235–250 (2022).

https://doi.org/10.1007/s11120-021-00877-5