DrawTexture RenderTexture

when i make a cube which use the stand shader named "Transparent/cutout/Diffuse"

and i make a new Camera which focuse the cube ,set the camera background color (255,255,255,0)

also it only render to texture ;

in the follow script using the rendertexture;
++++++++++++++++++++++++++++++++++++++
public Texture tex;//here using the rendertexture void OnGUI()
{
GUI.DrawTexture(new Rect(100, 200, 300, 300), tex, ScaleMode.ScaleAndCrop, true);

}

+++++++++++++++++++++++++++++++++++

but i can't see anythinig!


seems that if U set the alpha value of the camera's background color equals zero

and same time U use CutOUt shader

the result is U got nothing!