Abstract
Chloroplast NADH dehydrogenase-like (NDH) complex is structurally related to mitochondrial Complex I and forms a supercomplex with two copies of Photosystem I (the NDH-PSI supercomplex) via linker proteins Lhca5 and Lhca6. The latter was acquired relatively recently in a common ancestor of angiosperms. Here we show that NDH-dependent Cyclic Electron Flow 5 (NDF5) is an NDH assembly factor in Arabidopsis. NDF5 initiates the assembly of NDH subunits (PnsB2 and PnsB3) and Lhca6, suggesting that they form a contact site with Lhca6. Our analysis of the NDF5 ortholog in Physcomitrella and angiosperm genomes reveals the subunit PnsB2 to be newly acquired via tandem gene duplication of NDF5 at some point in the evolution of angiosperms. Another Lhca6 contact subunit, PnsB3, has evolved from a protein unrelated to NDH. The structure of the largest photosynthetic electron transport chain complex has become more complicated by acquiring novel subunits and supercomplex formation with PSI.
Highlights
Chloroplast NADH dehydrogenase-like (NDH) complex is structurally related to mitochondrial Complex I and forms a supercomplex with two copies of Photosystem I via linker proteins Lhca[5] and Lhca[6]
We found the NDH-dependent Cyclic Electron Flow 5 (NDF5) protein complex to be smaller in the mutants that were defective in Lhca[6], which is a linker protein that mediates supercomplex formation between NDH and PSILHCI
Like mitochondrial Complex I, consisting of 44 subunits in mammals[46], the chloroplast NDH complex consists of about 30 subunits in angiosperms[11,47], whereas the respiratory and photosynthetic NDH complex in proteobacteria and cyanobacteria consists of 14 and 18 subunits, respectively[7,8,48]
Summary
Chloroplast NADH dehydrogenase-like (NDH) complex is structurally related to mitochondrial Complex I and forms a supercomplex with two copies of Photosystem I (the NDH-PSI supercomplex) via linker proteins Lhca[5] and Lhca[6]. The latter was acquired relatively recently in a common ancestor of angiosperms. Our analysis of the NDF5 ortholog in Physcomitrella and angiosperm genomes reveals the subunit PnsB2 to be newly acquired via tandem gene duplication of NDF5 at some point in the evolution of angiosperms Another Lhca[6] contact subunit, PnsB3, has evolved from a protein unrelated to NDH.
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