We consider superstring sigma models that are based on coset superspaces G/H
in which H arises as the fixed point set of an order-4 automorphism of G. We
show by means of twistor theory that the corresponding first-order system,
consisting of the Maurer-Cartan equations and the equations of motion, arises
from a dimensional reduction of some generalised self-dual Yang-Mills equations
in eight dimensions. Such a relationship might help shed light on the explicit
construction of solutions to the superstring equations including their hidden
symmetry structures and thus on the properties of their gauge theory duals.Comment: v3: 16 pages, typos fixed and minor clarifications adde