Mechanosensitive ion channels are a diverse group of proteins likely present in all living organisms and are an essential mechanism for the perception of mechanical forces in cells. One family present in both plants and animals is the Piezo family. In animals, Piezo channels are plasma membrane-embedded calcium/cation channels that play essential roles in many developmental and physiological processes like vascular development, touch perception, and nociception. As very little is known about Piezo homologs in plants, we set out to determine the function of plant Piezo homologs using the moss Physcomitrella patens as our model. Knocking out two partially functionally redundant Piezo homologs led to reduced growth and altered morphology in tip-growing caulonema cells, which are responsible for colony spreading. In contrast to their plasma membrane-localized animal counterparts, both moss Piezo homologs localized to the vacuolar membrane. Using several vacuolar stains, we observed that vacuoles in the apical caulonema cells of double mutants were larger and more expanded, unlike the tubular vacuoles of the wild type caulonema cells. Our data thus show that Piezo proteins are involved in the maintenance of both vacuolar morphology and cell growth, but the exact underlying mechanisms are still unclear. As vacuoles are large calcium sinks and because animal Piezo channels conduct calcium, we are currently investigating the involvement of moss Piezo homologs in cytoplasmic calcium signaling. It appears that plant and animal Piezo homologs have diverged in both function and localization, which may reflect different needs for mechanoperception in the very distinct mechanical environment of animal and plant cells, e.g. presence of cell wall and thousand-fold higher osmotic pressures in the latter.
Coauthors: Ryan Richardson – Washington University in St. Louis;Ethan Weiner – Washington University in St. Louis;Magdalena Bezanilla – Dartmouth College;Elizabeth Haswell – Washington University in St. Louis