Unaffected by a vine gone wild (5)
I believe the answer is:
naive
'unaffected' is the definition.
(both can mean sincere or unpretentious)
'a vine gone wild' is the wordplay.
'a vine' anagrams to 'NAIVE'.
Though, I am not clear how this is indicated.
'by' is the link.
Can you help me to learn more?
(Other definitions for naive that I've seen before include "Too innocent or gullible" , "Ingenuous and credulous" , "Too credulous or trusting" , "Too simple and trusting" , "Innocent and credulous" .)