LOS ANGELES (Reuters) - Pop singer Kelly Rowland and Mexican singer-actress Paulina Rubio have signed onto "The X Factor" judging panel replacing Britney Spears and music mogul L.A. Reid, the Fox television talent competition produced by Simon Cowell said on Monday. Rowland, who rose to fame with R&B group Destiny's Child, and Rubio will be charged with re-igniting the Fox series that failed to stave off falling ratings after giving Spears a reported $15 million salary last year. Rowland, 32, and Rubio, 41, will join Cowell, 53, and pop singer Demi Lovato, 20, on the judging panel. ...