Barley Viridis-k links an evolutionarily conserved C-type ferredoxin to chlorophyll biosynthesis

Area of Science:

• Plant biochemistry
• Photosynthesis
• Chlorophyll biosynthesis

Background:

• Ferredoxins are crucial single-electron carriers in cellular processes.
• Chloroplast ferredoxins link photosystem I to NADPH production and other enzymes.
• Plant ferredoxins with C-terminal extensions, like FdC1 and FdC2, have poorly understood functions.

Purpose of the Study:

• To identify the function of a specific ferredoxin isoform with a C-terminal extension.
• To determine the role of the barley Viridis-k (VirK) gene in chlorophyll biosynthesis.
• To investigate the electron donor for the magnesium-protoporphyrin IX monomethyl ester cyclase.

Main Methods:

• Genetic analysis of barley mutants at the Viridis-k locus.
• Complementation assays using agroinfiltration (in vivo) and in vitro enzymatic assays.
• Biochemical characterization of the cyclase reaction and ferredoxin interaction.

Main Results:

• Barley mutants lacking the orthologous FdC2 gene (VirK) exhibit chlorophyll deficiency.
• VirK, but not canonical ferredoxin, complements the viridis-k phenotype in vivo.
• VirK demonstrated activity as an electron donor for the magnesium-protoporphyrin IX monomethyl ester cyclase in vitro.
• VirK accumulation is dependent on cyclase enzyme levels, suggesting a coordinated pathway.

Conclusions:

• VirK is an essential ferredoxin isoform specifically required for chlorophyll biosynthesis.
• VirK functions as the electron donor for the magnesium-protoporphyrin IX monomethyl ester cyclase.
• This finding assigns a specific role to C-type ferredoxins with C-terminal extensions in plants.