Project Details
Projekt
Studying the functional significance of the putative Na+/H+ carrier AtNHD1 in the thylakoid membrane for proton motive force dynamic and partitioning
Applicant
Professor Dr. Hans-Henning Kunz
Subject Area
Plant Physiology
Term
since 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 507704013
During photosynthesis, light energy drives charge separations within the photosystems. Electrons (e-) travel from H2O via a series of redox reactions to the e- acceptor NADP+. The process is coupled to proton (H+) deposition into the thylakoid lumen, which generates the proton motive force (PMF) that drives ATP synthesis. The PMF is partitioned into two energetically equivalent components, a pH gradient (ΔpH) and a membrane potential (Δψ). Their relative contribution is dependent on the light intensity and its dynamics. Low lumenal pH has also important protective implications, decreasing e- transport via the cytochrome b6f complex and activating energy dissipation as heat (qE), the main component of non- photochemical quenching (NPQ). Plants strike a balance between photoprotection and biomass gain by finetuning PMF partitioning. Ion transport proteins in the thylakoid membrane play a key role in this regard because H+ transfer into the lumen is coupled to a counter-ion flux that dissipates the membrane potential to allow for lumenal H+ accumulation. It follows that unraveling the thylakoid ion transportome is a prerequisite for our understanding of the PMF, photosynthetic productivity, and ultimately how to improve it. In the model plant Arabidopsis, transport proteins mediating Cl- flux (VCCN1) and K+/H+ exchange (KEA3) participate in PMF partitioning. At least one additional mediator for K+ or monovalent cation is expected in the thylakoid membrane. Recently, our group discovered that NHD1, a putative Na+/H+ exchanger, resides in the thylakoid and not in the envelope membrane as originally assumed. Heterologous expression of NHD1 restores growth of E. coli mutants defective in K+ transport, indicating NHD1 might facilitate K+ flux across thylakoid membranes in vivo. This project seeks to (i) determine the consequences caused by loss and gain of NHD1 function on PMF, photosynthesis, and global gene expression using Arabidopsis, (ii) to characterize NHD1 substrate specificity, and (iii) the design and spectroscopic characterization of higher order mutants devoid of NHD1, VCCN1, and KEA3 to update the current model of PMF dynamics and its molecular players under fluctuating light conditions. See also Graphical Abstract P06. Generally, our work will contribute to the overall aims of GoPMF 1, 2, and 5.
DFG Programme
Research Units
