As mentioned, the pressure you run should be dictated by the terrain. If you are on very hard packed then higher is better. If you ride over alot of rocks, soft soil, sand and such then a lower pressure will help with traction.
At 135 you could, well depending on what tires you are running, get away with pressure in the low 30's.
If you are running fatties (2.5 or larger) then you could easily run in the 20's. For XC I run 30 front and 35 rear and for DH I run 19 front/22 rear and I tip the scales at 275.
Just go out one day to a local trail, bring a floor pump and tire guage and play around with diff. pressures. Start with say 45 or so, do a quick run then drop it 2 psi. Because you are a light rider you may not notice any chage until you get down to around 34 but give it a shot and see what pressure you like the best.