It tells the story of an American student who falls in love with a young Muslim man on an idyllic island off the coast of Kenya before the clash of cultures complicates the relationship.Walker, daughter of The Color Purple author Alice, will co-produce the film.Madonna, whose previous films were WE and Filth and Wisdom, called the book "an incredible journey" last year.After it was published in October, the pop star posted a photo of the book cover and the message: "Read this book! An incredible journey! A beautiful LOVE story!"The romance will be co-produced by Bruce Cohen, who produced Silver Linings Playbook and American Beauty.Madonna and the producers are now searching for a screenwriter to adapt the book, according to The Hollywood Reporter.Madonna's last film was WE, about the relationship between Edward VIII and Wallis Simpson, which opened to several one-star reviews in the UK in 2011.The Hollywood Reporter said WE grossed a relatively low $583,000 (£352,000) at the US box office. It failed to make the top 10 in the UK.'A challenge'While promoting the film at Venice Film Festival in 2011, Madonna told BBC Arts Editor Will Gompertz making it had been "a bloody nightmare"."There wasn't anything easy about it, it was all a challenge," said the singer, who made her directorial debut with 2008's Filth and Wisdom.Since WE, Madonna has concentrated on her music career, with a number one album MDNA and huge world tour. She was named the world's top-earning celebrity by Forbes in 2013.The 55-year-old trumped the likes of Oprah Winfrey and Steven Spielberg to make an estimated $125m (£80m) from a combination of music, clothing and her fragrance lines.The magazine said it was Madonna's highest annual earnings since it began tracking earnings in 1999.(BBC)ANN.Az