Arabidopsis thylakoid formation 1 is a critical regulator for dynamics of PSII-LHCII complexes in leaf senescence and excess light

In higher plants, photosystem II (PSII) is a large pigment-protein supramolecular complex composed of the PSII core complex and the plant-specific peripheral light-harvesting complexes (LHCII). PSII-LHCII complexes are highly dynamic in their quantity and macro-organization to various environmental conditions. In this study, we reported a critical factor, the Arabidopsis Thylakoid Formation 1 (THF1) protein, which controls PSII-LHCII dynamics during dark-induced senescence and light acclimation. Loss-of-function mutations in THF1 lead to a stay-green phenotype in pathogen-infected and senescent leaves. Both LHCII and PSII core subunits are retained in dark-induced senescent leaves of thf1, indicative of the presence of PSII-LHCII complexes. Blue native (BN)-polyacrylamide gel electrophoresis (PAGE) and immunoblot analysis showed that, in dark-and high-light-treated thf1 leaves, a type of PSII-LHCII megacomplex is selectively retained while the stability of PSII-LHCII supercomplexes significantly decreased, suggesting a dual role of THF1 in dynamics of PSII-LHCII complexes. We showed further that THF1 interacts with Lhcb proteins in a pH-dependent manner and that the stay-green phenotype of thf1 relies on the presence of LHCII complexes. Taken together, the data suggest that THF1 is required for dynamics of PSII-LHCII supramolecular organization in higher plants.