Flower raised by American star (6)
I believe the answer is:
sirius
'star' is the definition.
(Sirius is the dog star)
'flower raised by american' is the wordplay.
'flower' becomes 'iris' (iris is a type of flower).
'raised by' shows that the letters should be reversed in order.
'american' becomes 'US' (United States).
'iris' back-to-front is 'siri'.
'siri'+'us'='SIRIUS'
(Other definitions for sirius that I've seen before include "The Dog Star, brightest of the fixed stars" , "The Dogstar" , "Brightest star in the sky" , "Prominent star" , "It's known as the Dog Star" .)