Arabidopsis PCR2 Is a Zinc Exporter Involved in Both Zinc Extrusion and Long-Distance Zinc Transport

Abstract

Plants strictly regulate the uptake and distribution of Zn, which is essential for plant growth and development. Here, we show that Arabidopsis thaliana PCR2 is essential for Zn redistribution and Zn detoxification. The pcr2 loss-of-function mutant was compromised in growth, both in Zn-excessive and -deficient conditions. The roots of pcr2 accumulated more Zn than did control plants, whereas the roots of plants overexpressing PCR2 contained less Zn, indicating that PCR2 removes Zn from the roots. Consistent with a role for PCR2 as a Zn-efflux transporter, PCR2 reduced the intracellular concentration of Zn when expressed in yeast cells. PCR2 is located mainly in epidermal cells and in the xylem of young roots, while it is expressed in epidermal cells in fully developed roots. Zn accumulated in the epidermis of the roots of pcr2 grown under Zn-limiting conditions, whereas it was found in the stele of wild-type roots. The transport pathway mediated by PCR2 does not seem to overlap with that mediated by the described Zn translocators (HMA2 and HMA4) since the growth of pcr2 hma4 double and pcr2 hma2 hma4 triple loss-of-function mutants was more severely inhibited than the individual single knockout mutants, both under conditions of excess or deficient Zn. We propose that PCR2 functions as a Zn transporter essential for maintaining an optimal Zn level in Arabidopsis.

Common Functions or Only Phylogenetically Related? The Large Family of PLAC8 Motif-Containing/PCR Genes

“…It has been shown that AtPCR1 expressing yeast cells take up less and that protoplasts isolated from antisense plants take up more cadmium, compared to control cells (Song et al, 2004). Similar observations were made for AtPCR2 expressing yeast cells, which also took up less zinc (Song et al, 2010). These results indicate that AtPCR1 and AtPCR2 act as heavy metal exporters.…”

“…Microarray results on the tissue-specific expression of AtPCR1 and 2 are not reliable, since the sequence used for the microarray analysis present in the public databases does not distinguish between the two. Promoter-reporter gene constructs revealed that AtPCR1 is expressed in stems, leaves, flowers and siliques but not in roots (Song et al, 2010). In young leaves it is exclusively expressed in trichomes, while in older leaves, AtPCR1 is expressed in all cells, although the strongest signal is still present in trichomes.…”

“…2010); ii) It has been shown that AtPCR forms homooligomers and may thus be able to form functional transporters as shown for the prokaryotic Mg 2+ transporter which is constituted by five identical subunits, each one having also only two α-helices; iii) triple knock-out plants in which, the two other transporters besides AtPCR2 essential for zinc transfer to the shoot, the P-type ATPases AtHMA2 and AtHMA4, were deleted exhibited an additive phenotype (Song et al, 2010). If AtPCR2 would deliver zinc to one of the HMAs the phenotype would not be additive; iv) the CCXXXXCPC motif is predicted to reside within the transmembrane region and is likely involved in the binding of divalent cations.…”

“…Experiments with AtPCR2 indicate that PCRs also can form oligomers. Song et al (2010) transformed yeast with two AtPCR2 constructs, containing different tags. It could be shown by immunoblots that the protein bands exhibiting a molecular weight higher than AtPCR2 indeed corresponded to homo-oligomers.…”

Influence of Soil Chemistry and Plant Physiology in the Phytoremediation of Cu, Mn, and Zn

“…However, other transporters can also perform the export of Zn to vascular tissues. In Arabidopsis, pcr2 lossof-function mutants accumulate Zn in roots, suggesting a role of in root-to-shoot translocation of Zn, independent of HMA2 and HMA4 (Song et al, 2010). Furthermore, it was proved that AtFRD3 is involved in loading Zn into xylem (Pineau et al, 2012).…”