how can I draw a connecting line between the label and the plot in R

A clean alternative would be to label the points directly, and remove the y-axis if wanted. e.g.:

ggplot(data, aes(x=0,y=Kingdom,color=Kingdom)) + 
  ggrepel::geom_text_repel(aes(label = Kingdom), vjust = -1,colour="black") + 
  geom_point(aes(size = Total),colour="blue",stroke=2) +
  scale_size(range = sizeRange)+ 
  theme_bw() + 
  theme(panel.border = element_blank(), 
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(), 
        axis.line = element_line(colour = "white"),
        axis.text.y=element_blank(),
        axis.title.y = element_blank(),
        axis.ticks.y=element_blank())