I would put a comma there because I'd put a comma between those clauses anyway:
"Laughter is America's most important export," is a well-known quote of Walt Disney's.
Laughter is America's most important export, as studies in global comedy economics show.
But you don't need to if you have a phrase or word that isn't a clause on its own.
Walter Elias "Walt" Disney claimed that laughter was "America's most important export".
We need not if we need not without the quotes:
"Laughter is America's most important export" that isn't covered by International trade agreements.
"Laugher is America's most important export" and K-Pop is America's most inexplicable import.
(A comma would be optional in the last).