ABSTRACT
The unicellular green alga Chlamydomonas reinhardtii is able to take up methylammonium/ammonium from the medium at different stages of its sexual life cycle. Vegetative cells and pre-gametes mostly used a low-affinity system (LATS) component, but gametes obtained after light treatment of N-deprived pre-gametes 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 analysed. We have found light regulation of four Amt1 genes: Amt1; 1, Amt1; 2, Amt1; 4 and Amt1; 5. Whereas light-dependent expression of Amt1; 1, Amt1; 2 and Amt1; 4 was independent of gametogenesis, and that of Amt1; 5 was activated in the lrg6 mutant, suggesting a connection between this transporter and the subsequent events taking place during gametogenesis.
Subject(s)
Chlamydomonas reinhardtii/metabolism , Chlamydomonas reinhardtii/radiation effects , Light , Quaternary Ammonium Compounds/metabolism , Biological Transport/radiation effects , Chlamydomonas reinhardtii/genetics , Chlamydomonas reinhardtii/growth & development , Gametogenesis, Plant/radiation effects , Gene Expression Regulation, Plant/radiation effects , Germ Cells, Plant/metabolism , Germ Cells, Plant/radiation effects , Kinetics , Methylamines/metabolism , Mutation/genetics , Plant Proteins/genetics , Plant Proteins/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Time FactorsABSTRACT
Chemotactic behavior of Chlamydomonas reinhardtii is altered during the sexual life cycle. Unlike vegetative cells and noncompetent pregametes, mature gametes did not show chemotaxis to ammonium. Loss of chemotaxis to ammonium in mating-competent cells is controlled by gamete-specific genes that are common for both mating-type gametes. Change of chemotaxis mode requires the sequential action of the two environmental signals: removal of ammonium from the medium and light. The mutants lrg1, lrg3, and lrg4 affected in the light-dependent step of sexual differentiation exhibited the loss of chemotaxis to ammonium in the absence of light. These data indicate that there are common components in the signaling pathways that control change of chemotactic behavior and forming of mating competence in gametes.
