  Baryon to meson transition distribution amplitudes (TDAs) extend the concept
of generalized parton distributions. Baryon to meson TDAs appear as building
blocks in the collinear factorized description of amplitudes for a class of
hard exclusive reactions, prominent examples of which being hard exclusive
meson electroproduction off a nucleon in the backward region and
baryon-antibaryon annihilation into a meson and a lepton pair. We study the
general properties of these objects following from the underlying symmetries of
QCD. In particular, the Lorentz symmetry results in the polynomiality property
of the Mellin moments in longitudinal momentum fractions. We present a detailed
account of the isotopic and permutation symmetry properties of nucleon to pion
(\pi N) TDAs. This restricts the number of independent leading twist \pi N TDAs
to eight functions, providing description of all isotopic channels. Using
chiral symmetry and the crossing relation between \pi N TDAs and \pi N
generalized distribution amplitudes we establish soft pion theorems for \pi N
TDAs, which determine the magnitude of \pi N TDAs. Finally, we build a simple
resonance exchange model for \pi N TDAs considering N and \Delta(1232) exchange
contributions into the isospin-1/2 and isospin-3/2 \pi N TDAs.
