Arabidopsis boron transporter for xylem loading

Abstract

Boron deficiency hampers the productivity of 132 crops in more than 80 countries. Boron is essential in higher plants primarily for maintaining the integrity of cell walls and is also beneficial and might be essential in animals and in yeast. Understanding the molecular mechanism(s) of boron transport is crucial for alleviating boron deficiency. Here we describe the molecular identification of boron transporters in biological systems. The Arabidopsis thaliana mutant bor1-1 is sensitive to boron deficiency. Uptake studies indicated that xylem loading is the key step for boron accumulation in shoots with a low external boron 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 fusion protein of BOR1 and green fluorescent protein (GFP) localized to the plasma membrane in transformed cells. The promoter of BOR1 drove GFP expression in root pericycle cells. When expressed in yeast, BOR1 decreased boron concentrations in cells. We show here that BOR1 is an efflux-type boron transporter for xylem loading and is essential for protecting shoots from boron deficiency.

Boron toxicity tolerance in wheat and barley: Australian perspectives

“…Bot1 was identified using an approach combining positional cloning and reverse genetics. Bot1 shows 58% identity to the orthologous Arabidopsis B transporter BOR1, required for xylem loading of B under conditions of low B supply (Takano et al 2002). Significantly, the barley 4H-derived tolerance mechanism identified in Sahara is naturally occurring, derived from an increase in Bot1 gene copy number and mRNA transcript abundance .…”

Cellular changes in boric acid-treated DU-145 prostate cancer cells

“…Boron is utilised by bacteria in the structure of several antibiotics and autoinducer-2, a signalling molecule utilised during interspecies quorum sensing (Chen et al, 2002;Semmelhack et al, 2004). Plants require the element for growth, flowering and seed formation, and obtain boron from soil pore water using a borate transporter, BOR1, expressed in root pericycle cells (Takano et al, 2002). A human homologue, the electrogenic, voltage-regulated, Na þ -coupled borate transporter NaBC1, was recently identified in human kidney tubular cells and may function to maintain plasma BA levels (Park et al, 2004).…”

Boron Nutrition and Chilling Tolerance of Warm Climate Crop Species

“…Boron loading into the xylem after passive uptake into root cells requires the function of B transporters (similar to a B transporter in animal cells; see Park et al, 2004) located in the plasma membrane of the root pericycle, particularly when external B levels are low (Takano et al, 2002). The recently suggested mechanism of active B uptake and transport in roots at low B supply (Dannel et al, 2000(Dannel et al, , 2002 may be related to the functions of these B transporters (Takano et al, 2002).…”

“…Murata and Nishiyama, 1998;Melis, 1999;Kratsch and Wise, 2000;Allen and Ort, 2001;Browse and Xin, 2001). Comparatively recent research findings have also greatly improved our understanding of B uptake and transport processes (Brown and Shelp, 1997;Hu and Brown, 1997;Blevins and Lukaszewski, 1998;Brown et al, 2002a;Frömmer and von Wiren, 2002;Takano et al, 2002) and B roles in cell wall formation, cellular membrane functions and anti-oxidation defence systems (Cakmak and Römheld, 1997;Matoh, 1997;Goldbach et al, 2002). However, much remains to be understood about how B nutrition modulates plant chilling tolerance and how chilling tolerance affects plant responses to low/deficient B supply, particularly at the cellular level.…”