You probably don't have a system problem. You probably had a slight cold snap last night, just enough to lose a little pressure in the tires, and by the time they warmed up, the issue was gone. That being said, one of your tires is a couple pounds light.
Check your tires, and if the light is still on, then look on the lower part of the dash, probably under the steering wheel on one side or the other for a reset button. I'm not sure exactly where it is on your car, but that's the usual place on most Toyota/Lexus.