extract a specific column in a nested list (extract from all sub lists)

[shamimashrafiyan]

I have a big list that has a lot of sub-lists.
I would like to search for a specific column name and extract that column from every sub-list.
for example: please see the attached image, I have a big list named "List1", it has several sub-lists, for example, "gene A", "gene B", ...., "gene N". each of these sublists has a list, for example, "gene A" has these columns: a, b, c, ...... . "gene B" has a, d, ... z.
How can I search "a" in all those sublists and finally reach all of them beside each other in a data frame?

[nirgrahamuk]

library(tidyverse)

(l1 <- list(
  gene_A = list(a=1:3,
                b=2:4,
                z=3:5),
  gene_B = list(a=9:7,
                b=8:6,
                c=7:5)
))

map_df(l1,
    ~pluck(.,"a"))

[shamimashrafiyan]

Thank you @nirgrahamuk , it worked.