Osmotic shrinkage of cells of Synechocystis sp. PCC 6803 by water efflux via aquaporins regulates osmostress-inducible gene expression

1 Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, 127276 Moscow, Russia 2 Department of Regulation Biology, National Institute for Basic Biology, Myodaiji, Okazaki 444-8585, Japan 3 Institute of Basic Biological Problems RAS, Pushchino, Moscow Region 142292, Russia 4 Department of Molecular Biomechanics, School of Life Science, The Graduate University of Advanced Studies, Myodaiji, Okazaki 444-8585, Japan Correspondence Dmitry A. Los losda{at}ippras.ru Osmotic stress causes water molecules to efflux from cells through the cytoplasmic membrane. This study reveals that targeted mutation of the aqpZ gene, encoding an aquaporin water channel protein, in the cyanobacterium Synechocystis sp. PCC 6803 prevents the osmotic shrinkage of cells, suggesting that it is the water channel rather than the lipid bilayer that is primarily responsible for water transition through the membrane of this organism. The observations suggest that the aquaporin-mediated shrinkage of the Synechocystis cells plays an important role in changes of gene expression in response to hyperosmotic stress. Abbreviations: EPR, electron paramagnetic resonance