Isolation of the Cytb6f-photosystem I complex from the thylakoid membrane of Arabidopsis thaliana

Photosynthetic organisms can in part adapt the photosynthetic machinery to changes in the light environment in a process termed state transition. An antagonistic pair formed by the STN7 kinase and the PPH1/TAP38 phosphatase participates in the regulation of state transition via phosphorylation (STN7 mutant locked in state 1) and dephosphorylation (PPH1 mutant locked in state 2) of LHCII subunits. The two assembly states of photosystem complexes have also been correlated with a transition of the photosynthetic electron flow from linear to cyclic (state 1 to 2) in Chlamydomonas reinhardtii. The assembly state of the complexes for energy and electron transfer in higher plants is not clear. Here, the function and assembly states of photosynthetic complexes from Arabidopsis thaliana were analyzed in vivo and in vitro. Mutant plants lacking either STN7 or PPH1 show distinct spectroscopic changes that indicate alterations in photosynthetic energy and electron transfer. Isolation of the photosynthetic protein complexes by free-flow interval zone electrophoresis and native PAGE and structural characterization by single particle analysis and mass spectrometry show a differential assembly of LHCII and of Cytb6f with Photosystem I.