Characterization of ion transport proteins involved in chloroplast function from land plants and algae
Abstract
Evolved around 2.4 billion years ago and even earlier, according to the new geochemical
evidence, oxygenic photosynthesis is the crucial turning point in the history of our planet.
Used by cyanobacteria, algae, and land plants, photosynthesis represents the most important
process in which absorbed sunlight is converted into the chemical energy and stored for later
use. From the moment photosynthesis appeared until today, photosynthetic organisms have
developed new and improved regulatory mechanisms to be able to cope with changes in light
intensity, nutrient availability, different temperatures, altitudes, etc.
Availability of nutrients (e.g., K+, Cl–, Mg2+) varies in the environment where photosynthetic
organisms live and with that also the internal concentration of ions within the organism’s
different compartments. To overcome such changes in the chloroplast, organelle specialized
in photosynthesis, several important processes and specialized proteins are required to
coordinate ion transport across different membranes and manage ion homeostasis.
This thesis answers a few important questions and reveals ion transporters and channels
involved in chloroplast function from land plants and green algae. These transport proteins
are either localized to the thylakoid membrane (Paper I, II, and III) or chloroplast inner
envelope (Paper IV) of Arabidopsis thaliana and Chlamydomonas reinhardtii.
Potassium and chloride fluxes across the thylakoid membrane are mediated by the K+
/H+
antiporter KEA3, the Cl− channel/transporter ClCe, and the voltage-dependent Cl− channel
VCCN1. In Paper I, we show that they act independently from each other in regulation of the
proton motive force (PMF), and adjust electron transport and non-photochemical quenching
(NPQ) at different light intensities. Paper II reveals one more important role of ClCe, namely
in state transitions, by regulation of the ATP synthase activity in conditions of low light. In
Paper III, we show that the Chlamydomonas bestrophin-like transporter BST4 when
introduced in Arabidopsis affects PMF, NPQ and ATP synthase activity by a mechanism
involving bicarbonate transport and interaction with RuBisCo. Paper IV reveals that the
envelope magnesium transporters MGR8, MGR9, and MGT10/MRS4 activate NPQ by a
mechanism building the pH gradient across the thylakoid membrane. MGT10/MRS4 also play
role in thylakoid ultrastructure.
Taken together, these findings help us to better understand the ion transporters across the
chloroplast inner envelope and thylakoid membrane and their role in regulation of
photosynthesis by different mechanisms.
Parts of work
I. Dukic E., Herdean A., Cheregi O., Sharma A., Nziengui H., Dmitruk D., Solymosi K., Pribil M., and Spetea C. (2019). K(+) and Cl(-) channels/transporters independently fine-tune photosynthesis in plants. Sci Rep 9(1), 8639. https://doi.org/10.1038/s41598-019-44972-z II. Dukic E., Gollan P., Grebe S., Herdean A., Aro E.M., and Spetea C. The Arabidopsis thylakoid chloride channel ClCe Regulates ATP availability for light-harvesting complex II protein phosphorylation. Submitted manuscript. III. Adler L., Dukic E., McCormick A., and Spetea C. Chamydomonas anion channel BST4 influences thylakoid membrane energization and photoprotection when expressed in Arabidopsis. Manuscript IV. Dukic E., Shaikh K.M., Fukuda K., van Maldegem K., Töpel M., Solymosi K., Hellsten J., Hansen T.H., Husted S., Higgins J., Sano S., Ishijima S. and Spetea C. Functional coordination of magnesium chloroplast transporters in the regulation of photosynthesis from plants and green algae. Submitted manuscript.
Degree
Doctor of Philosophy
University
University of Gothenburg. Faculty of Science.
Institution
Department of Biological and Environmental Sciences ; Institutionen för biologi och miljövetenskap
Disputation
Fredagen den 11 november 2022, kl10.00 i Hörsalen, Institutionen för biologi och miljövetenskap, Carl Skottsbergs gata 22B, Göteborg
Date of defence
2022-11-11
emilija.dukic@bioenv.gu.se
Date
2022-10-21Author
Dukic Marinkov, Emilija
Publication type
Doctoral thesis
ISBN
978-91-8069-037-9 (Print) and 978-91-8069-038-6 (PDF)
Language
eng