MSSM from SUSY Trinification
  We construct a $SU(3)^3$ supersymmetric gauge theory with a common gauge coupling g. Spontaneous breaking of this gauge group at a scale $M_X=1.3\times10^{16} $GeV gives naturally rise exactly to the Minimal Supersymmetric Standard Model $(MSSM)$ and consequently to the experimentally favored values of $sin^2\theta_w$ and $\alpha_s$.The gauge hierarchy problem is naturally solved by a missing-partner-type mechanism which works to all orders in the superpotential. The baryon asymmetry can be generated in spite of the (essential) stability of the proton. The solar neutrino puzzle is solved by the MSW mechanism. The LSP is a natural "cold" dark matter candidate and "hot" dark matter might consist of $\tau$-neutrinos. This model could be thought of as an effective $4d$ theory emerging from a more fundamental theory at a scale $M_c=M_P/\sqrt{8\pi}$ where $a_G\equiv{g^2\over{4\pi}}$ happens to be equal to unity. 
G. Lazarides and C. Panagiotakopoulos