Abstract
B is essential in higher plants and is also beneficial and maybe essential in animals and in yeast. The Arabidopsis thaliana mutant bor1-1 is sensitive to B deficiency. Uptake studies indicated that xylem loading is the key step for B accumulation in shoots at low external B supply and that the bor1-1 mutant is defective in this process. Positional cloning identified BOR1 as a membrane protein with homology to bicarbonate transporters in animals. Moreover, a BOR1::GFP fusion protein localized to the plasma membrane in transformed cells. The promoter of the BOR1 gene drove GFP expression in root pericycle cells. When expressed in yeast, BOR1 reduced B concentrations in cells. We show here that BOR1 is an efflux-type B transporter for xylem loading. To our knowledge, this is the first boron transporter identified in living organisms.
