Characterization of the genetic requirements for photoautotrophic growth under fluctuating light intensities, using novel high-throughput genomics approaches in the green alga Chlamydomonas reinhardtii
Final Report Abstract
Efficient conversion of energy is a critical challenge for all organisms. Energy in the environment is available either as chemical potential or light. Uniquely, the energy available as light can undergo extreme fluctuations. Little is known about how the photosynthetic process adjusts to rapid changes in light availability. Identifying the mechanisms that underlie efficient photosynthesis in dynamic light environments may uncover novel regulatory strategies and other central principles of robust photosynthetic energy conversion. As a DFG fellow, I could demonstrate with collaborators that Arabidopsis thaliana K+ efflux antiporter (KEA3) is critical for high photosynthetic efficiency upon transitions to low light. Upon a shift from dark to low light, or high to low light, kea3 mutants show prolonged dissipation of absorbed light energy as heat. KEA3 localizes to the thylakoid membrane, and its K+/H+antiport activity accelerates the downregulation of pH-dependent energy dissipation after transitions to low light, leading to faster recovery of high photosystem II quantum efficiency and increased CO2 assimilation. The activity of the KEA3 proton/potassium antiport domain is regulated by a C-terminal extension, which contains a conserved regulatory module. This C-terminus is localized in the thylakoid lumen and inhibits KEA3 activity in high light. Overexpression of KEA3 in Arabidopsis and tobacco results in accelerated photosynthetic acclimation from high to low light. Ongoing work elucidates, whether increased KEA3 activity can benefit plant yield in field conditions. Besides KEA3, also the conversion of the energy dissipating xanthophyll zeaxanthin at the thylakoid membrane plays an important role in the relaxation kinetics of pH-dependent energy dissipation after transitions to low light. I could show that in leaves a large fraction of the responsible enzyme Zeaxanthin epoxidase (ZEP) is localized to the thylakoid membrane, supporting a main function of ZEP in photosynthesis regulation in chloroplasts.
Publications
- (2014) High-Throughput Genotyping of Green Algal Mutants Reveals Random Distribution of Mutagenic Insertion Sites and Endonucleolytic Cleavage of Transforming DNA. The Plant Cell 26, 1398-1409
Zhang, R., Patena, W., Armbruster, U., Gang, S.S., Blum, S.R., Jonikas, M.C.
(See online at https://doi.org/10.1105/tpc.114.124099) - (2014) Ion antiport accelerates photosynthetic acclimation in fluctuating light environments. Nature Communications 5, 5439
Armbruster, U.,Carrillo, L.R., Venema, K., Pavlovic, L., Schmidtmann, E., Kornfeld, A., Jahns, P., Berry, J.A., Kramer, D.M., Jonikas, M.C.
(See online at https://doi.org/10.1038/ncomms6439) - (2015) Tissue-specific accumulation and regulation of zeaxanthin epoxidase in Arabidopsis reflect the multiple functions of the enzyme in plastids. Plant Cell Physiology56, 346-357
Schwarz, N., Armbruster, U., Iven, T., Brückle, L., Melzer, M., Feussner, I., Jahns, P.
(See online at https://doi.org/10.1093/pcp/pcu167)
