Efflux-type boron (B) transporter for xylem loading, responsive of boron translocation from roots to shoots under boron limitation (PubMed:16805739, PubMed:9390427, PubMed:12447444, PubMed:27449211). Boron is essential for maintaining the integrity of plants cell walls (PubMed:16805739, PubMed:9390427). Transferred from the plasma membrane via the endosomes to the vacuole under high-concentration of boron in a DRP1A-dependent manner (PubMed:16103374, PubMed:27449211, PubMed:20194745). Localized to the polar inner/stele-side domain of the plasma membrane under low-boron conditions, this polar localization is established after cell division (PubMed:27449211). Co-localizes with DRP1A in the cell plate and the plasma membrane (PubMed:27449211). Under boron excess, BOR1 is transferred from the plasma membrane via the endosomes to the vacuole for degradation in a DRP1A-dependent manner (PubMed:16103374, PubMed:27449211, PubMed:20194745). A number of isoforms are produced. According to EST sequences. Expressed in proximal side of various root cells, notably in the columella, lateral root cap, epidermis and endodermis in tip and elongation zones of the root (PubMed:27449211). Also detected in the epidermis, cortex, endodermis, and stele cells of the root hair zone (PubMed:27449211). Observed in cotyledons and hypocotyls (PubMed:27449211). First observed in seedlings and in the primary root tip and mature portion of the root (PubMed:27449211). Expressed in the basal region of the hypocotyl, localized with inner/stele-side polarity in the endodermal cells (PubMed:27449211). In the tip of cotyledons, accumulates mostly in epidermal cells of the top side, with a polar localization toward the inner side of the cotyledon (PubMed:27449211). High levels in the transition and differentiation zones of roots, localized with stele-side polarity in the epidermal and endodermal cells (PubMed:27449211). In the root meristem zone, present in epiderm, endoderm, columella, parts of the lateral cap, quiescent center (QC), vascular initial and protovascular cells (PubMed:27449211). In the QC, vascular initial and protovascular cells, exhibits an apical polar localization (PubMed:27449211). Belongs to the anion exchanger (TC 2.A.31.3) family.