  Boundary conditions on an extra-dimensional interval can be chosen to break
bulk gauge symmetries and to reduce the rank of the gauge group. We consider
this mechanism in models with gauge trinification. We determine the boundary
conditions necessary to break the trinified gauge group directly down to that
of the standard model. Working in an effective theory for the gauge
symmetry-breaking parameters on a boundary, we examine the limit in which the
GUT-breaking sector is Higgsless and show how one may obtain the low-energy
particle content of the minimal supersymmetric standard model. We find that
gauge unification is preserved in this scenario, and that the differential
gauge coupling running is logarithmic above the scale of compactification. We
compare the phenomenology of our model to that of four-dimensional trinified
theories.
