An [SU(3)]^4 Supersymmetric grand unified model
  We present a grand unified model based on the supersymmetric $SU(3)_L\otimes SU(3)_{CL}\otimes SU(3)_{CR}\otimes SU(3)_R$ gauge group, which unifies in one single step the three gauge couplings of the standard model at an scale $M\sim 10^{18}$ GeV, and spontaneously breaks down to $SU(3)_c\otimes U(1)_{EM}$ using only fundamental representations of SU(3). In this model the proton decay is highly suppressed and the doublet-triplet problem is lessened. The see-saw mechanism for the neutrinos is readily implemented with the use of an extra tiny mass sterile neutral particle for each generation which provides a natural explanation to the neutrino puzzle. 
Abdel P\'erez-Lorenzana and William A. Ponce