Niyogi Lab Research

False-color image of photosystem II efficiency in colonies of Chlamydomonas mutants that are unable to do photosynthesis. Photo credit: Robert Calderon

Oxygenic photosynthesis is the biological process that converts solar energy, carbon dioxide, and water into biomass and oxygen, and it is the defining metabolism of plants, algae, and cyanobacteria. Research in the Niyogi lab is focused on the regulation of photosynthesis and photoprotection, assembly and dynamics of photosynthetic membranes, and improvement of photosynthesis. 

Functional Genomics of Photosynthesis and Photoprotection in Chlamydomonas

green alga Chlamydomonas
The unicellular green alga Chlamydomonas reinhardtii is our model organism of choice for elucidating the detailed functions of genes involved in photosynthesis and photoprotection. Photosynthesis in Chlamydomonas is essentially identical to that in vascular plants, but unlike plants, Chlamydomonas can grow without photosynthesis, even in complete darkness. This ability allows for the isolation of mutants that are impaired in photosynthesis or in the mechanisms that protect the photosynthetic apparatus from photo-oxidative damage. Genetic tools available for Chlamydomonas include replica plating, tetrad analysis, and transformation of the nuclear and chloroplast genomes. An international Chlamydomonas genome project is identifying hundreds of new genes with potential roles in photosynthesis, and a challenge for the next decade is to determine the specific functions of these genes.

Regulation of Photosynthetic Light Harvesting by Nonphotochemical Quenching

Chlorophyll Plate
A major process involved in controlling photosynthesis in excessive light is the downregulation of photosystem II activity by pH- and xanthophyll-dependent de-excitation of singlet chlorophyll and dissipation of excess absorbed light energy as heat, measured as nonphotochemical quenching of chlorophyll fluorescence (NPQ). We are providing insights into the molecular mechanism of NPQ by isolating npq mutants of the laboratory weed, Arabidopsis thaliana. Characterization of a subset of these mutants has contributed to our knowledge of the role of xanthophyll pigments in NPQ. Other npq mutants identify components besides the xanthophylls that are critical for NPQ. For example, characterization of the npq4-1 mutant uncovered an essential role of the PsbS subunit of photosystem II in NPQ. Experiments with npq4-1 have shown that NPQ protects photosystem II from photoinhibition, especially in short-term high light.

Antioxidant Metabolism and Function

Chlorophyll Plate
Several antioxidant systems in algae and plants cope with ROS that are generated inevitably as byproducts of photosynthetic metabolism. Antioxidants in chloroplasts include small molecules such as carotenoids (xanthophylls and carotenes), tocopherols (vitamin E), ascorbate (vitamin C), and glutathione and enzymes such as ascorbate peroxidase (APX), superoxide dismutase (SOD), and alkyl hydroperoxide reductases. Many of the antioxidant small molecules that are made by algae and plants are also important nutrients in the human diet.

Light Stress Acclimation and ROS Signal Transduction

Except for the npq1lor1 double mutant, most of our npq and antioxidant-deficient mutants of Chlamydomonas and Arabidopsis are able to acclimate to high light over a period of several days. Thus, it is apparent that other photoprotective processes are able to compensate for the lack of NPQ and/or specific antioxidants. We are taking several approaches to identify these other photoprotective processes.