Wine-producing region -- cross central point (4)
I believe the answer is:
crux
'central point' is the definition.
(I've seen this in another clue)
'wine-producing region cross' is the wordplay.
'wine-producing region' becomes 'cru' (e.g. grand cru - vineyard or group of vineyards).
'cross' becomes 'x' (an X is a cross).
'cru'+'x'='CRUX'
(Other definitions for crux that I've seen before include "Particular difficulty" , "Baffling problem" , "Decisive point of an issue" , "Essence or gist" , "brain-teaser!" .)