在火山图中添加自定义图例

Question

我正在尝试绘制RNA序列中数据集的火山图。我想添加一个自定义图例，其中包含下调，上调和不下调的值，但我真的不知道该怎么做，也找不到在Google中做到这一点的方法（也许是我的问题这是我对R的经验不足。

这是我到目前为止的情节代码：

ggplot(df_toxins, aes(x = logFC, y = -log10(FDR))) +
      geom_point(data = subset(df_toxins, logFC > -1 & logFC < 1), 
                 color = "black", alpha = 0.6, size = 1.5) + 
      geom_point(data = subset(df_toxins, logFC < -1), 
                 color = "red", alpha = 0.5, size = 2.5) + 
      geom_point(data = subset(df_toxins, logFC > 1), 
                 color = "blue", alpha = 0.5, size = 2.5) +
      geom_vline(xintercept = c(-1, 1), linetype = "dashed") + 
      geom_hline(yintercept = 0) + 
      theme_linedraw() + 
      theme(plot.title = element_text(hjust = 0.5, size = 22)) + 
      ggtitle("Toxins")