Newly discovered algal enzyme could help improve efficiency of photosynthesis

For plants and algae that carry on photosynthesis, light can be too much of a good thing. On a bright, sunny day, a plant might only be able to utilize 20 percent or less of absorbed sunlight. 

The plant dissipates the excess light energy to prevent damage and oxidative stress, and a process called the xanthophyll cycle helps to flip the switch between energy dissipation and energy utilization.

"By manipulating photoprotection in plants, it may be possible to improve the efficiency of photosynthesis, and one potential outgrowth of that is higher crop productivity," said Krishna Niyogi, a faculty scientist in Berkeley Lab's Division of Molecular Biophysics and Integrative Bioimaging and a UC Berkeley professor of plant and microbial biology. "This is a relatively new and underappreciated area of exploration when it comes to understanding and improving photosynthesis."

The xanthophyll cycle involves the synthesis of a pigment called zeaxanthin – an antioxidant that gives corn its yellow color – from another pigment called violaxanthin. Violaxanthin de-epoxidase (VDE) is the key enzyme responsible for this process, which kicks into gear in the presence of excess light.

Niyogi and a postdoctoral researcher in his lab, Zhirong Li, recently identified a target in the photoprotection mechanism by studying the unicellular green alga Chlamydomonas reinhardtii, which is widely used as a model organism to study photosynthesis. The alga produced an enzyme called Chlorophycean VDE (CVDE) that was completely different from the other plant enzymes in the xanthophyll cycle. The researchers said the CVDE enzyme could be used to optimize photoprotection and thereby improve photosynthesis and crop productivity.