Characterisation of the role of PAM71, PAM71L and AtCGL20 in the biogenesis and function of photosystem II and the NAD(P)H dehydrogenase

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The assembly of the thylakoid multiprotein complexes photosystem II (PSII) and NAD(P)H dehydrogenase (NDH) proceeds through a number of distinct intermediate states and requires auxiliary proteins, the so-called assembly factors. We have previously identified and characterized the PSII assembly factor PAM68, and found in preparatory experiments that the sequence-related PAM68HL protein behaves like a NDH assembly factor. In addition, we found that lines with reduced expression of TerC, a protein essential for photosynthesis and plant development, as well as lines lacking the chloroplast protein PAM71, display phenotypes characteristic for PSII assembly mutants. We propose to characterize the proteins TerC and PAM71 and their association with PSII subunits and distinct assembly states, together with a detailed characterisation of the corresponding loss-of-function lines. To obtain a comprehensive picture of PSII assembly and the sequential action of PSII assembly factors, we will systematically analyse the interactions of TerC, PAM71 and PAM68 with PSII subunits, as well as with other PSII assembly factors, by the split-ubiquitin system, coim-munoprecipitation and bimolecular fluorescence complementation. Moreover, the role of PAM68HL in NDH assembly will be characterized by analysing loss-of-function lines and identifying interactors of PAM68HL by coimmunoprecipitation and bimolecular fluorescence complementation.