The gene presenilin (PS) in mammals provides the catalytic activity for an enzyme called gamma secretase, which cleaves, or cuts, important proteins Notch, Erb4 and the amyloid precursor protein (APP), all key components of communication channels that cells use to arbitrate functions during development. At the present time mutations in two mammalian genes are known to cause an earlier onset of Alzheimer’s. One is APP and the other is PS protein.  The enzyme gamma secretase contains PS at its core and works to dispose of proteins stuck in the cellular membrane. Gamma secretase mediates two cellular decisions- one is to cut APP and generate amyloid associated with Alzheimer’s and the other is to cut the Notch protein in response to specific stimuli. Notch is then free to enter the nucleus of cells where it partakes in regulating normal gene expression. Without Notch activity, a mammal has no chance of living. Notch is a part of a short-range mammalian communication channel, and for years it has been known to have a working relationship with PS.  However, Notch is absent in plant cells and the function of PS in plants was not elucidated until recently.  The moss plant Physcomitrella patens and its PS gene was studied in the laboratory of Ralph S. Quatrano, Ph.D. When the PS gene was removed the result was an obvious change — a phenotype. Moss lacking PS looked different, growing with straight, rigid filaments instead of curved and bent filaments like the parent moss with the PS gene intact. In moss, the mutant phenotypes suggest PS might play a role in signal gathering, cytoskeleton organization and/or cell wall composition and organization.  Inserting the moss PS gene in mammalian cells resulted in reversing some of the losses experienced by animal cells lacking PS function, testifying that the human and moss proteins had an evolutionary conserved function and structure.  Importantly, the human PS protein acted in plant cells even if its enzymatic activity was removed by mutation indicating that PS proteins in mammals can perform other functions besides the enzymatic ones, that is, outside its role as gamma secretase. The data from this outstanding plant model can be used not only to understand some of the off-target affects during Alzheimer’s Disease therapy, but also to unravel novel interactions and pathways in plants.