Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
Mol Biol Evol. 2012 Dec;29(12):3827-42. doi: 10.1093/molbev/mss193. Epub 2012 Jul 30.
Here, we present a study of the molecular evolution of the pheromone receptor genes (pre-1 and pre-2) in Neurospora taxa with different mating systems. We focus on comparisons between heterothallic and homothallic taxa, reproducing sexually by outcrossing and by intrahaploid selfing, respectively. Our general aim was to use a phylogenetic framework to investigate whether the evolutionary trajectory of the pheromone and receptor genes in Neurospora differs between heterothallic and homothallic taxa, and among the homothallic lineages/clades previously indicated to represent independent switches from heterothallism to homothallism in the evolutionary history of the genus. We complemented molecular evolution analyses with an expression study of the pre genes and their upstream regulators, the mating-type (mat) genes, in homothallic taxa. Our analyses suggest that the pheromone receptor gene pre-1 is functionally conserved in both heterothallic and homothallic taxa. Moreover, we found evidence of positive selection for a small fraction of codons in the cytoplasmic signal-transducing C-terminal region of the protein PRE-1. Distribution of positively selected codons differs between heterothallic and homothallic groups, suggesting functional divergence associated with mating system. The gene pre-2 was shown to evolve under high selective constraints, with no strong evidence for positive selection. Although our data suggest that both pre-1 and pre-2 are overall functional in homothallic taxa, individual taxa display frame-shift mutations causing premature stop codons, which might indicate loss of function. Transcriptional patterns of pre and mat genes in six homothallic taxa, selected to represent six different switches from heterothallism to homothallism, do not support a universal pattern of regulation of these genes during reproductive tissue development. Taken together, our analyses suggest that the pheromone receptor genes pre-1 and pre-2 are in general functional in homothallic Neurospora taxa, in contrast with the situation for the mat genes that are generally degenerate in these taxa.
在这里，我们研究了不同交配系统的Neurospora 分类群中信息素受体基因（pre-1 和 pre-2）的分子进化。我们专注于异宗配合和同宗配合分类群之间的比较，分别通过杂交和单倍体自交进行有性繁殖。我们的总体目标是使用系统发育框架来研究信息素和受体基因在Neurospora 中的进化轨迹是否在异宗配合和同宗配合分类群之间以及在同宗系/进化枝中有所不同，这些同宗系/进化枝先前被认为是该属进化历史中从异宗配合到同宗配合的独立转变。我们补充了分子进化分析，对同宗配合分类群中 pre 基因及其上游调节因子交配型（mat）基因进行了表达研究。我们的分析表明，信息素受体基因 pre-1 在异宗配合和同宗配合分类群中均具有功能保守性。此外，我们发现蛋白质 PRE-1 的细胞质信号转导 C 末端区域的一小部分密码子存在正选择的证据。正选择密码子的分布在异宗配合和同宗配合组之间存在差异，这表明与交配系统相关的功能分化。基因 pre-2 被证明在高选择压力下进化，没有强有力的正选择证据。尽管我们的数据表明 pre-1 和 pre-2 总体上在同宗配合分类群中具有功能，但个别分类群显示出导致过早终止密码子的移码突变，这可能表明功能丧失。六个同宗配合分类群的 pre 和 mat 基因的转录模式，选择代表从异宗配合到同宗配合的六个不同转变，不支持这些基因在生殖组织发育过程中普遍调节的模式。综上所述，我们的分析表明，信息素受体基因 pre-1 和 pre-2 在同宗配合的 Neurospora 分类群中通常具有功能，与 mat 基因的情况形成对比，这些基因在这些分类群中通常是退化的。
