Thioredoxin-insensitive plastid ATP synthase that performs moonlighting functions.

Area of Science:

• Plant Biology
• Biochemistry
• Photosynthesis Research

Background:

• Chloroplast ATP synthase is crucial for photosynthesis, catalyzing light-driven ATP synthesis.
• It plays a key role in feedback regulation of photosynthetic processes.
• Arabidopsis thaliana has two genes, ATPC1 and ATPC2, encoding homologous regulatory γ subunits.

Purpose of the Study:

• To investigate the distinct roles and regulation of the two γ subunits (γ(1) and γ(2)) of Arabidopsis chloroplast ATP synthase.
• To determine the functional differences between ATP synthase complexes containing γ(1) versus γ(2).

Main Methods:

• Analysis of various Arabidopsis mutants expressing different γ subunit combinations.
• Measurement of in vivo ATP synthesis activity under light and dark conditions.
• In situ redox titrations to assess the redox potential of regulatory thiol groups.

Main Results:

• Both γ(1) and γ(2) subunits can support photosynthetic ATP synthesis in vivo.
• In wild-type plants, only γ(1) is involved in photosynthetic ATP synthesis.
• γ(1)-ATP synthase exhibits light-induced redox regulation, while γ(2)-ATP synthase shows constant activity.
• γ(2)-ATP synthase has a higher redox potential for thiol/disulfide transition, remaining reduced under physiological conditions.

Conclusions:

• γ(2)-ATP synthase likely catalyzes ATP hydrolysis for proton translocation in nonphotosynthetic plastids, supporting processes like protein transport.
• ATPC2 expression in roots and its effect on root hair development support a role outside photosynthesis.
• Phylogenetic analysis indicates divergent evolution of ATP synthase complexes from an ancient gene duplication event.