Progress 09/01/10 to 08/31/12
Outputs
OUTPUTS: The work resulted in four publications (1-4). PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The overall goal of the work is to test the hypothesis that the chloroplast ATP synthase serves as a central regulator of the photosynthetic network. The ATP synthase is proposed to regulate both the light and dark reactions of photosynthesis, operating on downstream (dark) reactions and starch synthesis via its effects on inorganic phosphate (Pi) levels, while itself being regulated either directly by Pi or via metabolites working through a phosphorylation/14-3-3 system regulatory. We have achieved most of the research goals. In addition, the research has opened up several new (unexpected and exciting) research avenues that we continue to pursue. We have established that the chloroplast ATP synthase plays a key role in co-regulating the light and dark reactions of photosynthesis in both C3 and C4 plants. Defeating this regulation can speed up photosynthesis under optimal conditions, but results in photodamage to photosystem I under natural fluctuating environmental conditions. Our recent work on the cfq mutant of Arabidopsis suggests that Pi is not the major regulator of the ATP synthase. Improving the dynamic range of ATP synthase regulation may allow for higher productivity and higher resilience to environmental stress. Our most recent work led to the discovery two functionally distinct plastid ATP synthases in dicots. The ATP synthase normally functioning in photosynthesis contains one homolog of the γ subunit (γ1) which confers light-dark regulation via the thioredoxin system. We show that, in Arabidopis, when expressed, a second γ-subunit homolog (γ2) can also support photosynthetic ATP synthesis, has dramatically altered redox properties and is thus insensitive to thioredoxin regulation. We further show that γ2-ATP synthase is expressed in non-photosynthetic tissues and has a surprising role in root development. Eliminating γ2 leads to very short root hairs. When γ2 is overexpressed, root hairs become long. Finally, phylogenetic analysis suggests that γ2 originated from ancient gene duplication, resulting in divergent evolution of functionally distinct ATP synthase complexes in dicots. This work demonstrates that a naturally occurring ATP synthase lacks redox regulation, which is intriguing from both enzymatic and structural perspectives. Second, the localization of γ2 as well as effects of mutating or over-expressing this ATP synthase implies a previously unexpected function in non-photosynthetic tissues. Finally, these results represent clear evidence for divergent evolution of a multisubunit complex by modification of a single subunit, to meet multiple functional roles in certain plants. Participants Two Post-docs, Drs. Kaori Kohzuma and Atsuko Kanazawa, Four graduate students, Kenji Takizawa, Olavi Kiirats and Christopher Hall and Deserah Strand, and three undergraduate students, Heather Enlow and Amelia Abarhanovich and Mary Willard participated in experiments, screening mutants, growing plants and presenting their data in publications and conferences.
Publications
- Kohzuma, K., Dal Bosco, C., Kanazawa, A., Meurer, J., and Kramer, D. M. (2012) A Potential Function for the γ2 Subunit atpC2 of the Chloroplast ATP Synthase in Photosynthesis for Food, Fuel and Future (Kuang, T., Lu, C., and Zhang, L., Eds.), pp 193-196, Springer-Verlag, Beijing.
- Kohzuma, K., Dal Bosco, C., Kanazawa, A., Dhingra, A., Meurer, J., and Kramer, D. M. (2012) A thioredoxin-insensitive plastid ATP synthase that performs moonlighting functions, Proc Natl Acad Sci USA 109, 3293-3298.
- Kiirats, O., Kramer, D. M., and Edwards, G. E. (2010) Co-regulation of dark and light reactions in three biochemical subtypes of C4 species, Photosynth Res 105, 89-99.
- Kiirats, O., Cruz, J. A., Edwards, G., and Kramer, D. M. (2009) Feedback limitation regulates photosynthesis by modulating the activity of the chloroplast ATP synthase, Functional Plant Biology 365, 893-901.
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Progress 09/01/10 to 08/31/11
Outputs
OUTPUTS: In 2010-2011, the work resulted in two publications (1, 2) and one conference proceedings (3) PARTICIPANTS: Participants Two Post-docs, Drs. Kaori Kohzuma and Atsuko Kanazawa, Four graduate students, Kenji Takizawa, Olavi Kiirats and Christopher Hall and Deserah Strand, and three undergraduate students, Heather Enlow and Amelia Abarhanovich and Mary Willard participated in experiments, screening mutants, growing plants and presenting their data in publications and conferences. TARGET AUDIENCES: Scientific community interested in plant science, plant breeding for increased productivity. PROJECT MODIFICATIONS: Nothing to report.
Impacts
The overall goal of the work is to test the hypothesis that the chloroplast ATP synthase serves as a central regulator of the photosynthetic network. The ATP synthase is proposed to regulate both the light and dark reactions of photosynthesis, operating on downstream (dark) reactions and starch synthesis via its effects on inorganic phosphate (Pi) levels, while itself being regulated either directly by Pi or via metabolites working through a phosphorylation/14-3-3 system regulatory. We have achieved most of the research goals. In addition, the research has opened up several new (unexpected and exciting) research avenues that we continue to pursue. Overall, we have established that the chloroplast ATP synthase plays a key role in co-regulating the light and dark reactions of photosynthesis in both C3 and C4 plants. Defeating this regulation can speed up photosynthesis under optimal conditions, but results in photodamage to photosystem I under natural fluctuating environmental conditions. Our recent work on the cfq mutant of Arabidopsis suggests that Pi is not the major regulator of the ATP synthase. Improving the dynamic range of ATP synthase regulation may allow for higher productivity and higher resilience to environmental stress.
Publications
- Kohzuma, K, Dal Bosco, C, Kanazawa, A, Dhingra, A, Meurer, J, & Kramer, DM (2011) Proceedins of the National Academy of Sciences Minor revisions
- Kiirats, O, Kramer, D M, & Edwards, GE (2010) Photosynth Res 105, 89-99.
- Kohzuma, K, Dal Bosco, C, Kanazawa, A, Meurer, J, & Kramer, DM (2011) Proceedings of the 15th International Congress on Photosynthesis In Press.
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