Dope harvested from rainforest becomes most precious (4)
I believe the answer is:
info
'dope' is the definition.
(dope can informally mean information)
'harvested from rainforest becomes most precious' is the wordplay.
'INFO' is hidden in amongst the letters.
However, I am uncertain how this is indicated.
(Other definitions for info that I've seen before include "details" , "What's known" , "Facts (abbr)" , "counsel?" , "Facts; knowledge gained" .)