A rota devised for vital supplier (5)
I believe the answer is:
'vital supplier' is the definition.
'a rota devised' is the wordplay.
'devised' indicates an anagram.
'rota' anagrammed gives 'orta'.
'for' is the link.
(Other definitions for aorta that I've seen before include "claret supplier" , "Great artery in body" , "main arterial route" , "Main route from the heart" , "Main arterial vessel, carrying blood to the heart" .)