The Yang-Mills String as the A-Model on the Twistor Space of the Complex   Two-Dimensional Projective Space with Fluxes and Wilson Loops: the Beta   Function
  We argue that the string theory dual to a certain sector of the four-dimensional Yang-Mills theory at large-N is the A-model wrapping N-Lagrangian D-branes on the twistor space of the complex two-dimensional projective space, with certain fluxes and Wilson loops, by finding that the target-space beta function of this A-model coincides with the large-N beta function of the Yang-Mills theory 
Marco Bochicchio