The Zhang laboratory at the Donald Danforth Plant Science Center employs algal genomics and plant spectroscopy to study how photosynthetic organisms respond to high temperatures.
Global warming increases the frequency with which photosynthetic organisms are exposed to damaging high temperatures. Heat stress impairs plant growth and reduces crop yield. To engineer crops with higher thermo-tolerance, it is imperative to understand how photosynthetic cells sense and respond to high temperatures.
Photosynthesis uses sunlight energy to make food, and it is essential for agricultural production. However, photosynthesis is one of the most heat sensitive processes in plants. To meet the increasing global food demand for the future, we need to increase agricultural yield by engineering more robust and more efficient photosynthesis that can adapt to high temperatures. To achieve this goal, it is crucial to understand how photosynthesis responds to high temperatures and what factors limit its adaptation.
Project 1. Interrogate the functional genomic landscape of heat sensing and regulation in photosynthetic cells by using the eukaryotic, unicellular green alga Chlamydomonas reinhardtii.
Although heat responses in land plants have been studied for years, several major questions remain open, especially heat sensing and regulation. Despite some advances in understanding heat responses in land plants, studies of algal heat responses are largely limited. Algae have great potential to produce biofuels, but they frequently experience rapid and large temperature fluctuations in ponds or outdoor bioreactors that can severely impact algal growth and viability.
The eukaryotic, unicellular green alga Chlamydomonas reinhardtii is a great model to study how photosynthetic cells respond to high temperatures. A genome-saturating, indexed, mutant library of Chlamydomonas has been generated, facilitating both reverse and forward genetic screens under heat stress. Furthermore, a high-throughput and quantitative barcoding approach has been developed in Chlamydomonas, enabling tracking growth rates of individual mutants in pooled cultures and screening for heat-sensitive mutants at genome-wide scale.
By using these advanced tools and systems-wide omics studies in Chlamydomonas, we aim to understand how photosynthetic cells respond to high temperatures and identify a list of genes involved in heat sensing, regulation, and adaptation in photosynthetic cells. Novel genes identified in Chlamydomonas that have orthologs in land plants will be investigated to improve crop thermo-tolerance.
Project 2. Investigate the effects of high temperatures on photosynthesis in C4 plants.
High temperature increases photorespiration and reduces the efficiency of photosynthesis in C3 plants (e.g. wheat, rice, which produce three-carbon compound during the first step of photosynthetic CO2 fixation, C3 photosynthesis) . C4 plants (e.g. maize and sorghum, which produce four-carbon compound during the first step of photosynthetic CO2 fixation, C4 photosynthesis) uses two cell-types to concentrate CO2 and is more efficient than C3 photosynthesis in hot and dry environments. It is estimated that if C4 photosynthesis could be functional in C3 rice, the rice yield would be increased by at least 50%. A crucial step toward engineering C4 rice is to understand how C4 photosynthesis is regulated, especially under abiotic stresses, e.g. high temperatures. By using spectroscopic and other biochemical, genetic approaches, we aim to investigate how C4 photosynthesis (both light reaction and carbon fixation) is regulated under high temperatures by using C4 model plant Setaria viridis and C4 crop maize.