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Max Planck researchers in Cologne have discovered how protein kinases in
plants regulate adaptation to changing light conditions, October 2005.

The plant makes changes to its photosynthetic machinery and important
"protein gears". In the journal Nature (October 20, 2005), Max Planck
researchers have explained how two protein kinases ? that is, enzymes which
transfer phosphate groups to other proteins ? regulate how different kinds
of photosynthetic machinery do this adapting and make it possible for the
plant to adjust itself better under various lighting conditions.

Photosynthesis is a very complex process, and without it life on earth would
be extremely difficult, or possible only for exotic micro-organisms. Life
requires two molecules: carbon dioxide and water. The environment contains
large amounts of both. A plant sends both of these components through its
photosynthesis machinery, where they are combined, and sugar molecules are
synthesised. This sweet supplier of energy provides nourishment for the
plant and thus, indirectly, all forms of life.

There are three methods by which photosynthesis adapts when light conditions
change. The first is short-term adaptation, in which antennas, collecting
light, are altered within minutes. The second is long-term adaptation, in
which within days the composition and the relationships of the photosystems
to each other change. And the third is the phosphorylation of certain
proteins of photosystem II, which until now scientists assumed was necessary
for the replacement of defective photosynthetic proteins.

A small molecular helper, the protein kinase STN7, is responsible for the
first and second form of adaptation. A related kinase, STN8, is responsible
for the third. Although the function of STN7 in the first type of adaptation
has already been known, the research team from Cologne and Munich, with
support from Jena and Dusseldorf, were able to show that STN7 is also
necessary for the second form of adaptation. They were also able to clarify
the role of the enzyme STN8 for the third kind of adaptation.

The team, led by Dario Leister of the Max Planck Institute for Plant
Breeding Research, has thus reached a milestone in the research of the
adaptation of the photosynthesis mechanism in altered light conditions.

STN8 fundamentally modifies photosystem II, in which it phosphorylates
proteins. For a long time, this phosphorylation was considered important for
the replacement of defective proteins in the photosystem II. The researchers
were able to show, however, that the phosphorylation of proteins of
photosystem II is not crucial to their replacement. This has led to a new
question: why, then, is this phosphorylation necessary?

The researchers hope, in the future, to pursue this line of enquiry, and how
the STN7 kinase coordinates the short and long-term adaptation of
photosynthesis. In their report, the researchers were able to present the
first indications of an answer: phosphorylation of certain photosynthetic
proteins seems to be important for the regulation of special genes in
chloroplasts and cell nuclei.

[www.mpg.de]

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