title: The negative effect of nitrate on gametogenesis is independent of nitrate assimilation in Chlamydomonas reinhardtii.
abstract: The effect of nitrate on gamete differentiation as well as on the expression of genes involved in gametogenesis, nitrogen scavenging, and nitrate assimilation has been analyzed in wild-type and mutant strains of Chlamydomonas reinhardtii. Nitrate prevented gamete formation from wild-type strains and caused a strong reduction in the number of zygotes recovered in genetic crosses between nitrate-assimilation-deficient mutants, thus suggesting that nitrate by itself is providing a negative regulatory signal for the sexual differentiation of the alga. Addition of nitrate at low concentrations to wild-type cells, after an initial period of nitrogen starvation, resulted in a drastic decrease in transcript levels of both nitrate-assimilation genes (NIA1 and NRT2;1) and genes induced after N-starvation (NCG2 and NCG4). This strong effect of nitrate was due to its assimilation products since it was not evident in nitrate-assimilation mutants. A slight negative effect of nitrate on NCG4 expression was only observed in the mutant. Nitrate by itself was also found to provide a negative signal for the expression of gamete-specific genes (GAS3 and GAS18) in mutants incapable of assimilating nitrate.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba e Instituto Andaluz de Biotecnología, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Pozuelo
authors.forename: F
authors.initials: F
authors.lastname: Merchán
authors.forename: M I
authors.initials: MI
authors.lastname: Macías
authors.forename: C F
authors.initials: CF
authors.lastname: Beck
authors.forename: A
authors.initials: A
authors.lastname: Galván
authors.forename: E
authors.initials: E
authors.lastname: Fernández
mesh_terms: D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D003433:Crosses, Genetic; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D017125:Genes, Protozoan; D005854:Germ Cells / Q000502:physiology; D016296:Mutagenesis; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology*; D015053:Zygote / Q000187:drug effects / Q000502:physiology
chemical_list: D009566:Nitrates