Plant producing underwear is backed by state (8)
I believe the answer is:
brassica
'plant' is the definition.
The answer is an example.
'underwear is backed by state' is the wordplay.
'underwear' becomes 'bras'.
'backed' says the letters should be written backwards.
'by' is a charade indicator (letters next to each other).
'state' becomes 'ca' (abbreviation for California).
'is' back-to-front is 'si'.
'bras'+'si'+'ca'='BRASSICA'
'producing' is the link.
(Other definitions for brassica that I've seen before include "Cabbages, broccoli etc." , "Cabbages, cauliflowers etc" , "Plant genus including many vegetables" , "Swede perhaps" , "Plant of cabbage genus" .)