Company left with last and first letters with rapeseed (5)

'rapeseed' is the definition.
The answer and definition can be both plants as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'company left with last and first letters' is the wordplay.
'company' becomes 'co' (abbreviation).
'left' becomes 'l' (common abbreviation).
'with' means one lot of letters go next to another.
'last' becomes 'Z' (Last letter alphabet).
'first letters' says to take the initial letters.
The first letter of 'and' is 'a'.
'co'+'l'+'z'+'a'='COLZA'

'with' acts as a link.

Can you help me to learn more?