How to rotate a 2d line a 3d plot

So I have a 2d line in the xz plane, whose function I don't know, I want to rotate that line about the z axis. For example, if i have a straight line in the xz plane and i rotate it about the z axis I will get a cone.

I know I am suppose to use the rotation matrix;

R_z = (cos(theta),-sin(theta),0;sin(theta),cos(theta),0;0,0,1);

but my issuse is how do I display that rotated line as a surface plot.

Or would it be easier to transfer the 2d line into spherical coordinates, but I don't know how to plot spherical coordinates in Matlab.

Thanks