An efflux transporter is a membrane protein that moves substances out of a cell and into the surrounding space or another compartment. In plants, efflux transporters play a central role in nutrient transport, waste removal, hormone distribution, detoxification, and long-distance movement of minerals and metabolites.
Efflux transporters often work in coordination with influx transporters to create directional movement through tissues. A molecule may first enter a cell through an influx transporter and then be exported by an efflux transporter into the next cell layer or into the vascular system. This coordinated transport allows plants to move nutrients and signaling compounds from roots to shoots and between different organs.
A well-known example is Lsi2, the silicon efflux transporter found in the roots of many silicon-accumulating species. After monosilicic acid enters root cells through the influx transporter Lsi1, Lsi2 exports it from those cells toward the xylem, enabling transport to the shoots where silicon is ultimately deposited as solid silica.
Efflux transporters differ from influx transporters in the direction of movement. Together, they regulate the uptake, distribution, and compartmentalization of many substances throughout the plant.
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