  The form factors for the $B-->\pi$ transition are evaluated in the entire
momentum transfer range by using the constraints obtained in the framework
combining the heavy quark expansion and chiral symmetry for light quarks and
the quark model. In particular, we calculate the valence quark contributions
and show that it together with the equal time commutator contribution simulate
a B-meson pole q^2-dependence of form factors in addition to the usual vector
meson B^{*}-pole diagram for $B --> \pi l\nu$ in the above framework. We
discuss the predictions in our model, which provide an estimate of |V_{ub}|^2.
