Chemotaxis to ammonium and ammonium transport in Chlamydomonas

E.V. Ermilova1, M.M. Nikitin1, Zh. M. Zalutskaya1, T.V. Lapina1, E. Sanz-Luque2, and E. Fernández2

1Biological Research Institute of St. Petersburg University, Oranienbaumskoe schosse 2, Stary Peterhof, St. Petersburg, 198504 Russia; 2Department of Biochemistry and Molecular Biology, University of Córdoba, Campus de Rabanales, Edif. Severo Ochoa, bajo E/14071-Córdoba Spain

Chlamydomonas vegetative cells and pre-gametes display chemotaxis not only to ammonium but also to its toxic structural analogue - methylammonium. The results from competition experiments suggest that ammonium/methylammonium transporters are the primary participants in promoting ammonium/methylammonium chemotaxis probably depending on their respective affinities to each of these compounds. The data are clearly connected to the strong inhibition of methylammonium transport in mutant strain hat1, which resulted in the complete loss of chemotaxis to ammonium/methylammonium. Eight of the CrAmt1 genes encode the high-affinity transport systems for ammonium in Chlamydomonas cells. In wild type the expression patterns of Amt1.1-1.8 genes in the chemotactically active pre-gametes look similar to these in chemotactically inactive gametes. Therefore, loss of chemotaxis in gametes is not controlled by regulation of CrAmt1 at transcriptional level. The data obtained suggest that several ammonium transporters are involved in the initial events of signal transduction during chemotaxis to ammonium; the ammonium signal elicits not before but during or after ammonium transport; and chemotaxis in gametes is blocked in transduction pathway downstream from the signal perception step. (supported by INTAS N05-1000008-8004 and RFBR N07-04-00277).

e-mail address of presenting author: ermilova@ee6439.spb.edu