Stable accumulation of photosystem II requires ONE-HELIX PROTEIN1 (OHP1) of the light harvesting-like family
Plant Physiology Vol. 176, Issue 2 Feb 2018
Myouga F, Takahashi K, Tanaka R, Nagata N, Kiss AZ, Funk C, Nomura Y, Nakagami H, Jansson S, Shinozaki K

Abstract:
he cellular functions of two Arabidopsis one-helix proteins, OHP1 and OHP2 [also named light-harvesting-like Lil2 and Lil6, respectively, because they have sequence similarity to light-harvesting chlorophyll a/b-binding (LHC) proteins] remain unclear. Tagged null mutants of OHP1 and OHP2 (ohp1 and ohp2) showed stunted growth with pale-green leaves on agar plates, and these mutants were unable to grow on soil. Leaf chlorophyll fluorescence and the composition of thylakoid membrane proteins revealed that ohp1 deletion significantly affected photosystem II (PSII) core protein function and led to reduced levels of PSI core proteins; however, it did not affect LHC accumulation. Transgenic ohp1 plants rescued by OHP1-HA or OHP1-Myc proteins developed a normal phenotype. Using these tagged OHP1 proteins in transgenic plants, we localized OHP1 to thylakoid membranes, where it formed protein complexes with both OHP2 and High Chlorophyll Fluorescence 244 (HCF244). We also found PSII core proteins D1/D2, HCF136, and HCF173 and a few other plant-specific proteins associated with the OHP1/OHP2-HCF244 complex, suggesting that these complexes are early intermediates of PSII assembly. OHP1 interacts directly with HCF244 in the complex. Therefore, OHP1 and HCF244 play important roles in the stable accumulation of PSII.
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