Can a measurement of theta-13 tell us about quark-lepton unification ?
  We argue that a high precision measurement of the neutrino mixing parameter $\theta_{13}$, within a three neutrino seesaw framework can throw important light on the question of whether the quarks and leptons unify into a single matter at high scales. Based on a number of examples, we conclude that a value of $\theta_{13} \leq {\frac{\Delta m^2_{\odot}}{\Delta m^2_A}}\simeq 0.04$ would require at the minimum a pure leptonic interchange symmetry between $\mu$ and $\tau$ generations for its natural theoretical understanding and will disfavor a quark-lepton unification type theory such as those based on $SU(4)_c$ or SO(10) whereas a bigger value would leave open the possibility of quark lepton unification. 
R. N. Mohapatra