Bog I transformed into a desert! (4)
I believe the answer is:
gobi
'a desert' is the definition.
(I know that Gobi is a desert)
'bog i transformed' is the wordplay.
'transformed' indicates an anagram.
'bog'+'i'='bogi'
'bogi' with letters rearranged gives 'GOBI'.
'into' acts as a link.
(Other definitions for gobi that I've seen before include "very dry place" , "Arid region in central Asia, and 38 across" , "The . . . . Desert is a barren plateau of S Mongolia and N China" , "Dry spot" , "Desert, mostly in Mongolia" .)