It transports Parisians to Rome, perhaps, and about time! (5)
I believe the answer is:
metro
'it transports parisians' is the definition.
The definition suggests a singular noun which matches the answer.
'rome perhaps and about time' is the wordplay.
I cannot really see how this works, but
'time' could be 't' (abbreviation) and 't' is found in the answer.
an anagram of 'rome' is 'mero' which is located in the left over letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'to' is the link.
Can you help me to learn more?
(Other definitions for metro that I've seen before include "Parisian underground system" , "Parisian underground railway" , "Paris subway" , "The underground railway system in Paris" , "what moves many Parisians" .)