Protein phosphorylation and proteolysis - regulation and adaptive responses in photosynthesis

Jens Forsberg

Research output: ThesisDoctoral Thesis (compilation)

Abstract

Just as all other organisms, plants adapt to various environmental conditions. This work focuses on the role of chloroplast light harvesting complex II, LHCII, in adaptation of photosynthesis to changed light conditions.

The two photosystems of oxygenic photosynthesis, photosystem I and II, use light of slightly different wavelengths for photochemistry. Since the photosystems are coupled in series, a light favouring one photosystem over the other leads to unbalanced electron transport. This work describes how plants adapt to such unbalanced light by "state transitions". State transitions involve changing the distribution of the light harvesting antenna complex, LHCII, between the two photosystems. Using antibodies directed towards phosphotyrosine and phosphothreonine, we found that phosphorylation of LHCII on both tyrosine and threonine residues were inhibited by the tyrosine kinase inhibitor, genistein, at concentrations not expected to cause any direct effect on threonine kinase activity. Results from spectroscopic methods for monitoring state transitions in combination with genistein suggested that tyrosine kinase activity is required for the state 2 transition.

Phosphorylation of LHCII and expression of genes encoding certain proteins involved in photosynthesis have been shown to be controlled by the redox-state of the plastoquinone pool. It is however not known how the signals emanate from the plastoquinone pool. One hypothesis is that two-component systems are involved. We have identified nuclear genes encoding elements of two-component systems, whose gene products are predicted to be targeted to the chloroplast. Thus genomic evidence suggests that chloroplasts have retained this system for signal transduction. We also describe a phosphoprotein associated with photosystem II which becomes dissociated from it upon phosphorylation. This phosphoprotein might also be involved in signalling events.

Two novel chloroplast proteolytic activities are described. One of the activities is found in the stroma and the other one is associated with the thylakoid membranes. Both proteases responsible are capable of cleaving a recombinant LHCII N-terminal peptide. The stromal protease, which cleaves preferentially on the carboxy-side of glutamic acid, has been partially purified. The protease associated with the thylakoid membrane seems to be under redox-control and may be involved in the degradation of LHCII as plants adapt to high-light conditions.
Original languageEnglish
QualificationDoctor
Awarding Institution
  • Biochemistry and Structural Biology
Supervisors/Advisors
  • [unknown], [unknown], Supervisor, External person
Award date2002 Apr 11
Publisher
ISBN (Print)91-973969-1-5
Publication statusPublished - 2002

Bibliographical note

Defence details

Date: 2002-04-11
Time: 10:15
Place: Hall A, Center for Chemistry and Chemical Engineering, Lund

External reviewer(s)

Name: Anderson, Jan
Title: Professor
Affiliation: [unknown]

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Article: I - Race H.L., Forsberg J., Hind G. and Allen J.F. (1998) Photosystem II-associated protein kinase phosphorylates a novel 6.3 kDa protein which subsequently dissociates from photosystem II core complexes. In Garab, G. (ed), Photosynthesis: mechanisms and effects. Vol III, pp 1859-1863, Kluwer Academic Publishers, The Netherlands

Article: II - Allen J.F. and Forsberg J. (2001) Molecular recognition in the thylakoid structure and function. Trends in Plant Sci. 6, 317-326

Article: III - Forsberg J., Rosenquist M., Fraysse L. and Allen J.F. (2001) Redox signalling in chloroplasts and mitochondria: genomic and biochemical evidence for two-component regulatory systems in bioenergetic organelles. Biochem Soc Trans. 29, 403-407

Article: IV - Forsberg J. and Allen J.F. (2001) Protein tyrosine phosphorylation in the transition to light state 2 of chloroplast thylakoids. Photosynthesis Res. 6, 317-326

Article: V - Forsberg J., Kieselbach T., Ström J., Alexciev K., Allen J.F. and Åkerlund H-E. (2002) Protease activities in the chloroplast stroma and thylakoid membrane capable of cleaving an LHCII N-terminal peptide. (manuscript)

Subject classification (UKÄ)

  • Biological Sciences

Keywords

  • Växtbiokemi
  • proteolysis
  • Plant biochemistry
  • protease
  • two-component systems
  • protein kinase
  • protein phosphorylation
  • state transitions
  • light-harvesting antenna
  • photosynthesis
  • chloroplast

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