Conclusions
The data presented here reveal the potential for differential AtPIP2;1
CTD phosphorylation to be a key factor in the processes controlling
water and ion channel transport functions, in addition to localisation
trends. Mimicking a phosphorylated state of AtPIP2;1 S280 and S283 sites
resulted in a transport function where the Na+ and
K+ ion conductance reached a magnitude similar to that
observed for other plant ion channels expressed in X. laevisoocytes; indicating that phosphorylation-dependent ion flux through
AtPIP2;1 could hypothetically be significant in planta (McGaugheyet al., 2018). Plant aquaporins capable of facilitating ion
transport are key candidates for the elusive non-selective cation
channels responsible for a large proportion of Na+ and
K+ flux across the PM (Demidchik and Tester, 2002;
Rubio et al., 2010). Further testing is needed to explore the
influence of phosphorylation at S280 and S283 on water and ion transport
functions in planta , and to resolve whether the observations of
AtPIP2;1 potential to switch between ion and water channel modes are
applicable. Discovering the steps in the processes regulating the
switching between ion and water channel functions, and resolving their
relationship with osmotic stress tolerance mechanisms, holds great
potential for generating discoveries that support the engineering of
future strategies for improving plant productivity in dry and saline
environments.