  Local supersymmetry (SUSY) provides an attractive framework for the
incorporation of gravity and unification of gauge interactions within Grand
Unified Theories (GUTs). Its breakdown can lead to a variety of models with
softly broken SUSY at low energies. In this review article we focus on the SUSY
extension of the Standard Model (SM) with an extra U(1)_{N} gauge symmetry
originating from a string-inspired E_6 grand unified gauge group. Only in this
U(1) extension of the minimal supersymmetric standard model (MSSM) inspired by
E_6 GUTs the right-handed neutrinos can be superheavy providing a mechanism for
the generation of the lepton and baryon asymmetry of the Universe. The particle
content of this exceptional supersymmetric standard model (E_6SSM) includes
three 27 representations of the E_6 group, to ensure anomaly cancellation, plus
a pair of SU(2)_W doublets as required for gauge coupling unification. Thus
E_6SSM involves extra exotic matter beyond the MSSM. We consider symmetries
that permit to suppress non-diagonal flavour transitions and rapid proton
decay, as well as gauge coupling unification, the breakdown of the gauge
symmetry and the spectrum of Higgs bosons in this model. The possible Large
Hadron Collider (LHC) signatures caused by the presence of exotic states are
also discussed.
