Functional divergence of the NIP III subgroup proteins involved altered selective constraints and positive selection

Background  

Nod26-like intrinsic proteins (NIPs) that belong to the aquaporin superfamily are unique to plants. According to homology modeling and phylogenetic analysis, the NIP subfamily can be further divided into three subgroups with distinct biological functions (NIP I, NIP II, and NIP III). In some grasses, the NIP III subgroup proteins (NIP2s) were demonstrated to be permeable to solutes with larger diameter, such as silicic acid and arsenous acids. However, to date there is no data-mining or direct experimental evidences for the permeability of such larger solutes for dicot NIP2s, although they exhibit similar three-dimensional structures as those in grasses. It is therefore intriguing to investigate the molecular mechanisms that drive the evolution of plant NIP2s.