Uncle has to see about this plant (6)
I believe the answer is:
'this plant' is the definition.
(sesame is a kind of plant)
'uncle has to see' is the wordplay.
I cannot quite understand how this works, but
'uncle' could be 'sam' (Uncle Sam is an example) and 'sam' is found in the answer.
'to see' could be 'see' (seeing is a kind of seeing) and 'see' is present in the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'about' acts as a link.
Can you help me to learn more?
(Other definitions for sesame that I've seen before include "Open .... is a pantomime cry" , "Oil plant from Ali Baba's cry" , "which magically opens" , "Oil-producing plant" , "Plant with oil-rich seeds" .)