Probing the role of photosystem II phosphorylation in chloroplasts
File(s)
Author(s)
Riaz, Saba
Type
Thesis
Abstract
Reversible phosphorylation of the D1, D2, CP43 and PsbH core subunits of Photosystem II (PSII) in plants and green algae is widely assumed to fine-tune the repair of damaged PSII complexes by facilitating the disassembly of damaged PSII dimeric complexes and remodelling of the thylakoid membrane to permit efficient migration from the appressed membranes in the grana to the stroma lamellae for repair. Studies on PSII phosphorylation often use the Arabidopsis stn7/stn8 double knock-out mutant, which lacks key kinases. However, these kinases also target other proteins like PGLR1A, CAS, CURT1, and TAC16. A more refined approach to study the role of PSII core phosphorylation is to generate single or multiple mutants lacking the phosphorylation sites in D1, D2, CP43 and PsbH. In Chapter 3 I show that mutation of the phosphorylation site of D1 at residue Thr2 (mutant D1-T2A) does not affect growth of tobacco under normal laboratory growth conditions and has no dramatic effect on the ability to repair PSII. The height, diameter and number of the grana are also unaffected in the D1-T2A mutant. In Chapter 4, I investigate the role of PsbH phosphorylation in marker-free tobacco mutants lacking the phosphorylation site at Thr5 (PsbH-T5A mutants) and show that PSII repair, state transitions and the thylakoid ultrastructure are comparable to that in WT tobacco. In Chapter 5 I examine the role of the phosphorylation site of CP43 in tobacco at residue Thr-3. The CP43-T3M mutant grows photoautotrophically but accumulates fewer PSII super-complexes than WT suggesting a role in assembly or stability. In Chapter 6, I show that the N-terminal tail of PsbH of the green alga Chlamydomonas reinhardtii is dispensable for PSII activity. Overall, the findings in my thesis provide new information on the role of phosphorylation in PSII assembly and repair.
Version
Open Access
Date Issued
2024-12-05
Date Awarded
2025-05-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Nixon, Peter
Publisher Department
Department of Life Sciences
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)