  We demonstrate the existence of topologically nontrivial phase in a
one-dimensional fermionic lattice system subjected to synthetic gauge fields,
which is beyond the standard Altland-Zirnbauer classification of topological
insulators. The topological phase can be characterized by the presence of
degenerate zero-mode edge states or a quantized Berry phase of the occupied
Bloch band. By analyzing symmetries of the system, we identify that the
topological phase and zero-mode edge states are protected by two hidden
symmetries. An extended model with hidden symmetry breaking is also studied in
order to reveal the effect of hidden symmetries on the symmetry protected
topological phase.
