Wanda Sykes Quits 'Roseanne' Producing Gig Due to Roseanne's Racist Tweet

Wanda Sykes is following Whitney Cummings out the door of "Roseanne" -- but her exit is a direct response to Roseanne Barr's racist attack on an Obama aide, a woman who's a close friend of Wanda's ... TMZ has learned.

Wanda kept it short and sweet, saying ... "I will not be returning to ['Roseanne']." The timing is no coincidence, coming within an hour of Barr's apology for calling an Obama adviser the product of "muslim brotherhood & planet of the apes."

A source close to Wanda tells us Roseanne's tweet is "100 percent why [Wanda] quit." We're told Wanda and Valerie Jarrett, the Obama adviser, are friends ... and hung out together as far back as 2009, when Wanda hosted the White House Correspondents' Dinner.

Wanda was a consulting producer on the hugely successful reboot, which is returning for a second season -- but, clearly, with some producing changes.