Light control of ammonium transport in Chlamydomonas reinhardtii
Zhanneta M. Zalutskaya1, Ekaterina S. Minaeva1, 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
The unicellular green alga Chlamydomonas reinhardtii is able to take up methylammonium/ammonium from the medium at different stages of its sexual life cycle. C. reinhardtii undergoes gametogenesis when signals of nitrogen deficiency and light are acting. Vegetative cells and mating incompetent pregametes (obtained from vegetative cells in nitrogen-free medium in the dark) mostly used a low-affinity system (LATS) component, but gametes obtained after light treatment of N-deprived pregametes, expressed both LATS and high-affinity system (HATS) components for the uptake of methylammonium/ammonium. The activity of the LATS component was stimulated by light in only 5 min in a process independent of protein synthesis. By using the lrg6 mutant that produces sexually competent gametes in the dark, light effects on ammonium transport and gamete differentiation have been separately analyzed. The light regulation of ammonium uptake observed during conversion of pregametes into gametes appears to be independent of light control of gametogenesis, since mutant lrg6 shows sexually competent gametes in the dark and still has the light regulation of ammonium uptake. C. reinhardtii has the largest AMT1 family of ammonium transporters so far described, consisting of eight members. We can conclude from the present work that light controlled expression of genes Amt1;1, 2 and 4 in C. reinhardtii occurs simultaneously with that of HATS by a mechanism independent of gametogenesis, and that expression of Amt1; 5 appeared to occur together with sexual cell differentiation. (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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