Authorises at last the transplantation of the roses (8)
I believe the answer is:
endorses
'authorises' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their -s form.
Maybe they are linked in a way I don't understand?
'at last the transplantation of the roses' is the wordplay.
'at' is a charade indicator (letters next to each other).
'last the transplantation' becomes 'end' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'roses' with letters rearranged gives 'orses'.
'end' put next to 'orses' is 'ENDORSES'.
Can you help me to learn more?
(Other definitions for endorses that I've seen before include "'Supports, backs (8)'" , "One dress (anag.)" , "Approves, supports" , "Countersigns, approves" , "Gives support or approval to" .)