In photosynthetic systems of cyanobacteria and plants, pigment-binding proteins are responsible for the absorption of light energy. Antenna pigments (chlorophyll and carotenoids) harvest light energy, and rapidly transfer this absorbed light energy to nearby pigments and eventually to the reaction center. The main purpose of the proteins is to keep the pigments in their proper location and orientation, so that energy transfer is efficient and rapid.

In plants the chlorophyll a/b binding proteins (Cab proteins) serve as the main light harvesting antenna, however, cyanobacteria only bind chlorophyll a and therefore lack these Cab proteins. But recently also in cyanobacteria relatives to the Cab gene family have been identified. In the complete sequenced genome of Synechocystis we identified five genes that are predicted to code for small polypeptides similar to parts of the Cab proteins. We called these proteins small Cab-like proteins (SCP) and their genes have been named scp genes.

The assembly of chlorophyll to the chlorophyll-binding proteins has to be regulated very carefully: in the absence of chlorophyll the proteins are degraded immediately and in the absence of protein free chlorophyll has a potentially damaging photooxidative activity in light. Most steps in chlorophyll biosynthesis are well studied, but it is still not known how the chlorophyll is transported after biosynthesis to the different chlorophyll-binding proteins. Some members of the Cab proteins, e.g. the early light induced proteins (ELIPs), have been suggested as chlorophyll-carriers. In cyanobacteria the small relatives, the SCP:s could serve in a similar function. Chlorophyll carrier proteins should posses the ability to bind pigments transiently. The uptake and release of chlorophyll should be easy and these proteins should also bind carotenoids to protect the cell from photooxidative damage.

In my group we investigate about the presence of these chlorophyll-carrier proteins in plants and cyanobacteria.

• Do pigment-carrier proteins exist?
• How is chlorophyll synthesis regulated?
• How is newly synthesized chlorophyll stored and transferred to newly synthesized chlorophyll-binding proteins?

Senescence is interesting from many theoretical perspectives; however, it is also of practical value as a factor in plant productivity and post-harvest life-time. In order to understand senescence and to manipulate it for economic purposes, it will be essential to identify and understand the genes that initiate and carry out senescence.

 

Using the facilities of the Umeå Plant Science Centre we want to study the role of proteases in leaf senescence in the tree poplar in comparison to the annual plant Arabidopsis thaliana and the cyanobacterium Synechocystis sp. PCC . The aim of our studies on senescence are firstly, to identify and clone genes encoding proteases that are involved in the senescence process, to characterize these genes, their gene products and the mode of regulation using DNA microarray chips and the proteomic approach and to determine their function, specificity and localization with the help of molecular and biochemical methods. The creation of trees with increased yield or hardiness is our final goal.

 

Xu, H., Vavilin, D., Funk, C., Vermaas, W. () Multiple deletions of small Cab-like proteins in the cyanobacterium Synechocystis sp.PCC : consequences for pigment biosynthesis and accumulation. J. Biol. Chem., in press.

 

Thidholm, E., Lindström, V., Tissier, C., Robinson, C., Schröder, W.P. and Funk, C. () Localisation of PsbW and PsbS in the photosystem II dimer. FEBS Lett. 513, 217-222.

 

Xu, H., Vavilin, D., Funk, C. and Vermaas, W. () Small CAB-like proteins regulating tetrapyrrole biosynthesis. Plant Mol. Biol. 49, 149-160.

 

Funk, C. () The PsbS protein: A Cab-protein with a function of its own. In: Advances in Photosynthesis: Regulation of Photosynthesis (Aro, E.-M. and Andersson, B. eds.), Vol. 11, Kluwer Academic Publisher, The Netherlands, 453-467.

 

Funk, C. and Vermaas, W.F.J. () Expression of Cyanobacterial Genes Coding for Single-Helix Polypeptides Resembling Regions of Light-Harvesting Proteins from Higher Plants. Biochemistry 38, .