Create a node with your color channel
Create a node with your alpha/transparency channel
Connect the color channel using drag and drop (with MMB*), select Diffuse
Connect alpha transparency using drag and drop (with MMB*), select Other. Maya opens a new window with two columns: on the left column it displays the channels of your texture node, on the right column you see the channels of your mia_material_x_passes.
If your texture channel for the transparency is a image with alpha, select on the left, the outAlpha channel and then on the right, select the cutoutOpacity channel (you can find it deeper on the list, is one of the last channels..).
Otherwise if your texture channel for the transparency is a b/n image as rgb basis, expand on the left the outColor channel, select outR and then on the right, select the cutoutOpacity channel (you can find it deeper on the list, is one of the last channels..).
*MMB = Middle Mouse Button.ù
