You will be fine. With that psu you can power anything just about, so are not limited to a r9 290, you can choose whatever gpu your budget will allow, be it a 290 or gtx980ti. Your mobo is sufficient for any modern gpu.
PCI Express 3.0 x16. That's all you need, and thats exactly what you have. The only drawback will be the cpu. If your cpu/apu isn't sufficiently powerful to keep up with the top range gpus, you'll have spent money for nothing, so just be advised that a r9 390/gtx970 is about as strong as you'll need, but a good match for the better fm2 cpus. If you have an a4, a 290/290x/380 or gtx960 would be a better match up.
GL.