  We investigate differences and similarities between fundamental fermions and
adjoint fermions in SU(N) gauge theories. The gauge theory with fundamental
fermions possesses ZN symmetry only in the limit of infinite fermion mass,
whereas the gauge theory with adjoint fermions does have the symmetry for any
fermion mass. The flavor-dependent twisted boundary condition (FTBC) is then
imposed on fundamental fermions so that the theory with fundamental fermions
can possess ZN symmetry for any fermion mass. We show similarities between FTBC
fundamental fermions and adjoint fermions, using the Polyakov-loop extended
Nambu--Jona-Lasinio (PNJL) model. In the mean-field level, the PNJL model with
FTBC fundamental fermions has dynamics similar to the PNJL model with adjoint
fermions for the confinement/deconfinement transition related to ZN symmetry.
The chiral property is somewhat different between the two models, but there is
a simple relation between chiral condensates in the two models. As an
interesting high-energy phenomenon, a possibility of the gauge symmetry
breaking is studied for FTBC fundamental fermions.
