This region has been named the SPX domain after (Syg1, Pho81 and XPR1). The domain is found at the amino terminus of a variety of proteins. The PHO1 gene family conserved in plants is involved in a variety of processes, most notably the transport of inorganic phosphate from the root to the shoot of the plant and mediating the response to low levels of inorganic phosphate. More recently it has become evident that PHO1 gene families have diverged in various plants and may play roles in stress response as well as the stomatal response to abscisic acid.