Jubilant journalist backs upcoming story (6)
I believe the answer is:
elated
'jubilant' is the definition.
(I know that jubilant can be written as elated)
'journalist backs upcoming story' is the wordplay.
'journalist' becomes 'ed' (short for editor).
'backs' means one lot of letters go next to another.
'upcoming' is a reversal indicator.
'story' becomes 'tale' (synonyms).
'tale' in reverse letter order is 'elat'.
'ed' after 'elat' is 'ELATED'.
(Other definitions for elated that I've seen before include "Cock-a-hoop" , "Jubilant, happy and excited" , "Euphoric" , "Ecstatically happy" , "Puffed with success" .)