Heteromerization of plant aquaporins

Abstract

The discovery of PIP (plasma membrane intrinsic protein) heterotetramerization has opened a new field of research. This phenomenon was first observed between PIPs belonging to two phylogenetic groups (PIP1 and PIP2) with ubiquitous expression in different plant tissues. These isoforms present few differences in their primary sequence but show major differences in their functionality when expressed in heterologous systems. Many reports in recent years shed light on the PIP1 and PIP2 interaction as a regulatory mechanism to modulate their trafficking and biological activity. In this regard, PIP heterotetramerization has been proposed as a way of achieving a diversification in the water transport capacity and in the control of net solute transport. Also, acidification conditions were shown to act as a mechanism to control the opening and blockage of these channels in native tissues, and their proton-dependent gating can be affected depending on the presence of PIP2 homotetramers or PIP1-PIP2 heterotetramers in the target membrane.In the present chapter we report the state-of-the-art knowledge about PIP heterotetramerization in the context of protein oligomerization. We emphasize the main experiments that help to understand the existence of some relevant structural elements involved in PIP oligomerization and the conditions necessary for these hetero-oligomers to occur in the cell.