Abstract
Arabidopsis thaliana BOR1, an efflux-type boron transporter, plays a major role in xylem loading of boron. For evaluating the physiological importance of pericycle specific expression of BOR1 in roots, transgenic Arabidopsis plants expressing BOR1 under control of cauliflower mosaic virus 35S RNA promoter were generated. When T2 plants were grown on kanamycin(Km) medium with 3μM boric acid, but not with 30μM, some of the plants resistant to Km showed growth inhibition similar to bor1-1 mutant. This was observed in several independent transgenic lines. Western analysis and microscopic observation confirmed overexpression of BOR1 in all types of cells in roots. We propose BOR1 proteins, expressed in outer layers of cells in roots, exported boron prior to xylem loading and inhibited transport of boron to shoots.
