Harmonic Superspaces from Superstrings
  We derive harmonic superspaces for N=2,3,4 SYM theory in four dimensions from superstring theory. The pure spinors in ten dimensions are dimensionally reduced and yield the harmonic coordinates. Two anticommuting BRST charges implement Grassmann analyticity and harmonic analyticity. The string field theory action produces the action and field equations for N=3 SYM theory in harmonic superspace. 
P. A. Grassi (YITP, Stony Brook, DISTA, Univ. Piem. Orien.) and P. van   Nieuwenhuizen (YITP, Stony Brook)