Minute new role for fungi (5)
I believe the answer is:
morel
'fungi' is the definition.
'minute new role' is the wordplay.
'minute' becomes 'm' (abbreviation).
'new' indicates anagramming the letters.
'role' with letters rearranged gives 'orel'.
'm'+'orel'='MOREL'
'for' acts as a link.
(Other definitions for morel that I've seen before include "Edible mushroom" , "One has a cap" , "Edible fungus" , "Type of mushroom" .)