The Zhang laboratory at the Donald Danforth Plant Science Center employs algal genomics and plant spectroscopy to study how photosynthetic organisms respond to their environment.
Photosynthesis uses sunlight energy to make food and it is essential for agricultural production. Adverse and fluctuating environments in the field frequently decrease the efficiency of photosynthesis in crops. 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 challenging environments. To achieve this goal, it is crucial to understand how photosynthesis responds to adverse environments and what factors limit its adaptation. How photosynthesis is regulated under changing environment is poorly understood.
The Zhang laboratory will work on two main research topics:
1. Interrogate the functional genomic landscape of heat sensing in photosynthetic cells by using a genome-saturating, indexed, algal mutant library and a quantitative phenotyping tool.
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.
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 has several advantages over land plants to study heat stress: (1) Heat stress can be applied homogeneously to all cells in liquid cultures; (2) It only has two heat shock factors (Arabidopsis has 25), thus facilitating forward and reverse genetic approaches; (3) Vegetative cells are haploid therefore mutant phenotypes show up immediately; (4) Cells grow very fast with 6~8 h doubling time; (5) All three genomes (nucleus, chloroplast, mitochondrion) of Chlamydomonas are sequenced and transformable; (6) The unicellular nature of Chlamydomonas enables high-throughput approaches and functional genomics.
A genome-saturating, indexed, mutant library of Chlamydomonas has been generated, facilitating both reverse and forward genetic screens under various conditions. 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 mutants of interesting phenotypes under various conditions.
By using these advanced and exciting tools in Chlamydomonas, we aim to identify a list of genes involved in heat sensing, regulation, and adaptation. Novel genes identified in Chlamydomonas that have orthologs in higher plants will be investigated in higher plants to improved crop thermo-tolerance.
2. Explore the regulation of photosynthetic electron transport in C4 plants.
High temperature increases photorespiration and reduces the efficiency of C3 photosynthesis. 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. The light reaction of C4 photosynthesis is essential yet under-explored.
By using spectroscopic and other biochemical, genetic approaches, we aim to investigate these questions: (1) How does the light reaction of C4 photosynthesis respond to changing environment, such as temperature fluctuations and water availability? (2) How is the light reaction regulated during the development of C4 photosynthesis? Both C4 crop maize and C4 model plant Setaria will be used to address these important questions.