Chemotaxis of Chlamydomonas reinhardtii to nitrate
Zhanneta M. Zalutskaya1, Tatyana V. Lapina1, Emilio Fernandez2 and Elena V. Ermilova1
1) Laboratory of Adaptation in microorganisms, Saint-Petersburg State University, Oranienbaumskoe schosse 2, Stary Peterhof, St. Petersburg, 198504 Russia
2) Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias, Campus de Rabanales, Edificio Severo Ochoa Planta baja, Universidad de Córdoba, Spain
Nitrate plays an important role in the nitrogen metabolism of most cells, including Chlamydomonas reinhardtii. We have shown that vegetative cells of C. reinhardtii are attracted by nitrate. Potassium did not act as an attractant for motile cells. Nit2 mutant was found to exhibit normal chemotaxis to nitrate. The data suggest that chemotaxis events appear to be specific and independent of those involved in nitrate assimilation. During sexual differentiation C. reinhardtii changes its chemotactic behavior not only to ammonium but also to nitrate. Unlike vegetative cells and noncompetent pregametes, mature gametes did not show chemotaxis to nitrate. Loss of chemotaxis to nitrate in mating-competent cells is controlled by gamete-specific genes that are common for both mating-type gametes. Just like gamete formation, the change in chemotaxis mode is controlled by the sequential action of two environmental cues, removal of nitrogen from the medium and light. A mutant (lrg6) that exhibits light-independent gamete formation was shown also to switch off chemotaxis to nitrate in the dark. Comparative analysis of wild-type and RNAi20 strain with reduced level of phototropin has indicated that the control of chemotaxis to ammonium and to nitrate during gametogenesis may share mechanisms and that switch-off of chemotaxis towards attractants - nitrogen sources is dependent on phototropin. The data support our hypothesis that chemotaxis in gametes is blocked in the transduction pathway downstream from the transport/signal perception step, possibly at the flagellar level. (This work was supported by the grant N10-04-00156 from RFBR and from Ministerio de Ciencia e Innovacion (Spain) BFU-2008-1798).
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