The negative effect of nitrate on gametogenesis is independent of nitrate assimilation in Chlamydomonas reinhardtii
The negative effect of nitrate on gametogenesis is independent of nitrate assimilation in Chlamydomonas reinhardtii
复制标题
硝酸盐对莱茵衣藻配子发生的负面影响与硝酸盐同化无关
作者：
M. Pozuelo;F. Merchán;M. Macías;C. Beck;A. Galván;E. Fernández
摘要：在莱茵衣藻野生型和突变株中，研究了硝酸盐对配子分化以及配子发生、氮清除和硝酸盐同化相关基因表达的影响。 硝酸盐防止配子形成的野生型菌株，并引起了强烈的减少，在硝酸盐同化缺陷突变体之间的遗传杂交中恢复的合子的数量，从而表明，硝酸盐本身是提供一个负调控信号的性分化的ESTA。在氮饥饿的初始阶段后，向野生型细胞中添加低浓度的硝酸盐，导致硝酸盐同化基因（NIA 1和NRT 2;1）和氮饥饿后诱导的基因（NCG 2和NCG 4）的转录水平急剧下降。硝酸盐的这种强烈作用是由于其同化产物，因为它在硝酸盐同化突变体中不明显。硝酸盐对NCG 4表达的轻微负面影响仅在突变体中观察到。硝酸盐本身也被发现提供一个负信号的配子特异性基因（GAS 3和GAS 18）的表达突变体不能同化硝酸盐。
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.