Source: MICHIGAN STATE UNIV submitted to NRP
COREGULATON OF THE LIGHT AND DARK REACTIONS OF PHOTOSYNTHESIS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
Reporting Frequency
Annual
Accession No.
0225377
Grant No.
2008-35318-30376
Cumulative Award Amt.
(N/A)
Proposal No.
2011-01178
Multistate No.
(N/A)
Project Start Date
Sep 1, 2010
Project End Date
Aug 31, 2012
Grant Year
2011
Program Code
[56.0C]- Plant Biology (C): Biochemistry
Recipient Organization
MICHIGAN STATE UNIV
(N/A)
EAST LANSING,MI 48824
Performing Department
Plant Research Laboratory
Non Technical Summary
The control of photosynthesis is important for plant productivity and survival. We have shown that the chloroplast ATP synthase (the enzyme that stores a large fraction of solar energy in plants) is an important control point for photosynthesis. Our proposed research is aimed at determining how this enzyme regulates photosynthesis and how it might be monitored or modified to improve productivity.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2032499100050%
2062499100050%
Goals / Objectives
Photosynthesis must thus be balanced over rapid and slow time scales to both meet the energy needs of plants while avoiding deletrious side reactions. This balancing is critically important for crop energetics. This proposal aims to identify and characterize key regulatory mechanisms in this balancing regulatory network. Here we present preliminary data showing a strong link between the sink capacity of plants (e.g. how fast they can grow and much starch they can make) and the regulation of the ATP synthase, both at the level of biochemical interactions and expression of proteins. These data suggest that the ATP synthase plays a key role in a feedback-regulation network involving the light and dark reactions of photosynthesis, adjusting photosynthesis to balance productivity with avoidance of photodamage. As such, it may be an important target for engineering to improve photosynthetic productivity or resistance to stress. We propose that the ATP synthase operates on downstream reactinos in this network via its effects on inorganic phosphate (Pi) levels, while itself being regulated either directly by Pi or via metabolites working through 14-3-3 system. The major open questions that we address here are: How is the ATP synthase integrated into the overall regulatory network of photosynthesis And What regulates the ATP synthase
Project Methods
Our work thus far has demonstrated that the ATP synthase plays an important role in regulating photosynthesis, balancing efficiency with the avoidance of photodamage, while potentially playing a key role in regulating starch synthesis. In the remaining year of the proposed work, we will focus on understanding the factors that regulate the ATP synthase under different conditions, and will be guided by important clues given by our work thus far. We will address two major questions: 1) Does the ATP synthase play a key role in a regulatory network that includes AGPase that sets the photosynthetic strategy of the plant 2) Is the ATP synthase regulated by Pi, as has been suggested for some time, or by a new mechanism, e.g. a 14-3-3 system To address these questions, we will take particular advantage of new in vivo spectroscopic probes and the development of new lines with modified ATP synthase or sink limitations. Using these tools, we will test for relationships among ATP synthase activity, the light and dark reactions of photosynthesis that will distinguish among possible models and to determine the extents to which photosynthetic efficiency can be modulated.

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.


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.