PCI-e 3.0 compatibility

So... I have been waiting patiently for the GTX 600 series to show itself, this after the GTX 580 I bought literally exploded.

Anyway, I had a horrible thought. The new series cards are PCI-e 3.0. I'm pretty sure my mobo (P55A UD3) only supports 2.0/2.1

So, this is probably a dumb question, but will a PCI-e 3.0 card still work in my machine? Or am I going to have to upgrade to a new mobo/stick with the GTX 500 series


Thanks guys