Protistology 4 (4) 301-310 (2006/7)
Characterization of phototropin-controlled signaling components that regulate chemotaxis towards ammonium in
Chlamydomonas
Elena V. Ermilova,1 Zhanna M. Zalutskaya,1 Darya M. Baibus1 and
Christoph F. Beck 2
1 Laboratory of Microbiology, Biological Research Institute
of St. Petersburg State University, St. Petersburg, Russia
Summary
Absorption of blue light by phototropin results in the activation of signaling pathways that control the
switch-off of chemotaxis during gametogenesis, the conversion of pregametes to gametes, and the maintenance of
mating competence in gametes. Pregametes were treated with pharmacological compounds to test their effect on the
light-induced switching-off of chemotaxis. The data obtained suggest that a protein kinase C-like component acts as
negative regulator early in the signaling pathway while a tyrosine protein kinase and a protein kinase A are needed
to transduce the signal downstream from this protein kinase C-like component. The defect of a strain with reduced
phototropin levels that, upon irradiation, showed attenuated inactivation of chemotaxis could be corrected by the
application of protein kinase C inhibitors or protein kinase A activators, supporting the hypothesis that these
protein kinases are components of a phototropin-controlled signaling pathway. A mutant (lrg6) that exhibits
light-independent gamete formation was shown also to switch off chemotaxis in the dark. Treatment of this mutant
with inhibitors of either tyrosine protein kinase or protein kinase A prevented the switch-off of chemotaxis in the
dark, suggesting that the LRG6 gene product acts upstream from both protein kinases. A comparison of the components
that make up the three phototropin-controlled signaling pathways operating during sexual differentiation revealed
that the chemotaxis-specific route appears to employ moduls from both the pathway that controls gamete formation and
the one controlling maintenance of mating ability.
Key words: cAMP, chemotaxis, Chlamydomonas, phototropin, protein kinases
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