<title>Abstract</title>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 <italic>NDF5</italic> ortholog in Physcomitrella and angiosperm genomes reveals the subunit PnsB2 to be newly acquired via tandem gene duplication of <italic>NDF5</italic> 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.