Plant 14-3-3 proteins assist ion channels and pumps

Turgor pressure is a cellular parameter, important for a range of physiological processes in plants, like cell elongation, gas exchange and gravitropic/phototropic bending. Regulation of turgor pressure involves ion and water transport at the expense of metabolic energy (ATP). The primary pump in the plasma membrane (the H(+)-ATPase) is a key player in turgor regulation since it provides the driving force for ion uptake, followed by water influx through osmosis. Using the phytotoxin fusicoccin (a well-known activator of the ATPase) as a tool, 14-3-3 proteins were identified as regulators of the H(+)-ATPase. Since fusicoccin has a dramatic effect on K(+) accumulation and cellular respiration as well, we studied whether 14-3-3 proteins play a role in the regulation of the mitochondrial F(0)F(1)-ATP synthase and ion channels in the vacuolar and plasma membranes. Besides the plasma membrane H(+)-ATPase, we have identified thus far at least four other transport proteins that are regulated by 14-3-3 proteins. The mechanism of regulation will be described and the possibility that 14-3-3 proteins act as coordinators of ion transporters with varied but interdependent functions will be discussed.