  In this work we study spectra of $^7$Be, $^7$Li, $^8$Be and elastic
scattering cross sections $^4$He($^3$He, $^3$He)$^4$He, $^4$He($^3$H,
$^3$H)$^4$He within the Gamow shell model (GSM) in the coupled-channel
formulation (GSM-CC). The evolution of channel amplitudes and the alignment of
the many-body state with the decay channel in the vicinity of the channel
threshold is studied for selected states. The GSM-CC in multi-mass partition
formulation applied to a translationally invariant Hamiltonian with an
effective finite-range two-body interaction reproduce well the spectra of
$^7$Be, $^7$Li, $^8$Be and elastic scattering reactions: $^4$He($^3$He,
$^3$He)$^4$He, $^4$He($^3$H, $^3$H)$^4$He. Detailed analysis of the dependence
of reaction channel amplitudes on the distance from the particle decay
threshold allowed to demonstrate the alignment of the wave function in the
vicinity of the decay threshold. This analysis also demonstrates the appearance
of clustering in the GSM-CC wave function in the vicinity of the cluster decay
threshold. We demonstrated that GSM formulated in the basis of reaction
channels including both cluster and proton/neutron channels allows to describe
both the spectra of nuclei with low-energy cluster thresholds and the
low-energy elastic scattering reactions with proton, $^3$H, and $^3$He
projectiles. Studying dependence of the reaction channel amplitude in a
many-body state on distance from the threshold, we showed an evolution of the
$^3$He, $^4$He clustering with increasing separation energy from the cluster
decay threshold and demonstrated a mechanism of the alignment of many-body wave
function with the decay threshold, i.e. the microscopic reorganization of the
wave function in the vicinity of the cluster decay threshold which leads to the
appearance of clustering in this state.
