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 ${\theta }_{13}\le \frac{\mathrm{\Delta }{m}_{\odot }^2}{\mathrm{\Delta }{m}_A^2}\simeq 0.04$ 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.