By Piya Sinha-Roy INDIO, California (Reuters) - A slew of rising artists and bands kicked off the annual Coachella Valley Music and Arts Festival on Friday, ahead of the much anticipated reunion of hip-hop duo Outkast headlining the first night of the three-day festival. Grammy-winning Outkast, formed by Atlanta rappers Andre 3000 and Big Boi, last worked together on 2006 album "Idlewild." But ahead of their headlining set late on Friday, music lovers watched artists such as Ellie Goulding, Grouplove, ZZ Ward and Aloe Blacc perform in the open field of the festival, against the backdrop of the Southern California desert. Coachella is the first major festival of the summer live music scene, and is often an important stop for an artist on the rise, as the festival has helped launch artists into the U.S. mainstream industry. Recent success stories include Florence + The Machine, and electronic music DJs Skrillex and Calvin Harris, the latter two both returning this year.