Abstract
Arabidopsis has three PsbQ-Like (PQL) proteins in addition to the PsbQ subunit of the oxygen-evolving complex (OEC) of photosystem II. Recent proteomic and in silico co-expression studies suggested that the two PQL proteins, PQL1 and PQL2, might have a function in the chloroplast NAD(P)H dehydrogenase (NDH) complex. In this study, we report the characteristics of Arabidopsis mutants lacking either of two PQLs, pql1 and pql2. The NDH activity estimated by chlorophyll fluorescence analysis was severely decreased in pql1 and pql2 mutants, indicating that both PQLs are required for the NDH activity. In thylakoid membranes of the wild-type plants, PQLs were tightly associated with the NDH complex and protected from protease treatments, while unassembled PQLs were unstable in the mutants lacking known NDH subunits, NdhB or PsbP-Like protein 2 (PPL2). Defect of PQL1 caused drastic reduction of the known NDH subunits in pql1 mutant, while the NDH subunits were partially stable in pql2 mutant, indicating that the functional role and the binding site in the NDH complex would be differed between PQL1 and PQL2.
