Pollinator beginning to transform vegetable (4)
I believe the answer is:
beet
'vegetable' is the definition.
(I know that beet is a type of vegetable)
'pollinator beginning to transform' is the wordplay.
'pollinator' becomes 'bee' (I've seen this in another clue).
'beginning to' indicates taking the first letters.
The first letter of 'transform' is 't'.
'bee'+'t'='BEET'
(Other definitions for beet that I've seen before include "Crop plant, sugar source" , "An edible root plant" , "Root used as a source of sugar" , "Source of food" , "Root, maybe source of sugar" .)