Evolution of an assembly factor-based subunit contributed to a novel NDH-PSI supercomplex formation in chloroplasts

Area of Science:

• Plant molecular biology
• Photosynthesis research
• Evolutionary biology

Background:

• The chloroplast NADH dehydrogenase-like (NDH) complex is structurally similar to mitochondrial Complex I.
• NDH forms a supercomplex with Photosystem I (PSI) via linker proteins Lhca5 and Lhca6.
• Lhca6 was recently acquired in angiosperm evolution.

Purpose of the Study:

• To identify and characterize the role of NDH assembly factors in Arabidopsis.
• To investigate the evolutionary origins of NDH subunits and their assembly mechanisms.
• To understand the structural and functional integration of NDH with PSI.

Main Methods:

• Genetic analysis of NDH assembly in Arabidopsis mutants.
• Bioinformatic analysis of NDF5 orthologs and subunit evolution in plant genomes.
• Biochemical characterization of NDH-PSI supercomplex formation.

Main Results:

• NDH-dependent Cyclic Electron Flow 5 (NDF5) functions as a key NDH assembly factor in Arabidopsis.
• NDF5 initiates the assembly of NDH subunits (PnsB2, PnsB3) and the linker protein Lhca6.
• The NDH subunit PnsB2 arose from a duplication of NDF5 in angiosperm evolution.
• The Lhca6 contact subunit PnsB3 evolved from an unrelated protein.

Conclusions:

• NDF5 plays a crucial role in the initial steps of NDH complex assembly.
• The evolution of the NDH-PSI supercomplex involved the acquisition of novel subunits and assembly factors.
• Understanding NDH assembly provides insights into the increasing complexity of photosynthetic electron transport chains.