AUTHOR=Li Bo , Qiu Jiaen , Jayakannan Maheswari , Xu Bo , Li Yuan , Mayo Gwenda M. , Tester Mark , Gilliham Matthew , Roy Stuart J. 

TITLE=AtNPF2.5 Modulates Chloride (Cl−) Efflux from Roots of Arabidopsis thaliana

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.02013

DOI=10.3389/fpls.2016.02013

ISSN=1664-462X

ABSTRACT=<p>The accumulation of high concentrations of chloride (Cl<sup>−</sup>) in leaves can adversely affect plant growth. When comparing different varieties of the same Cl<sup>−</sup> sensitive plant species those that exclude relatively more Cl<sup>−</sup> from their shoots tend to perform better under saline conditions; however, the molecular mechanisms involved in maintaining low shoot Cl<sup>−</sup> remain largely undefined. Recently, it was shown that the NRT1/PTR Family 2.4 protein (NPF2.4) loads Cl<sup>−</sup> into the root xylem, which affects the accumulation of Cl<sup>−</sup> in Arabidopsis shoots. Here we characterize NPF2.5, which is the closest homolog to NPF2.4 sharing 83.2% identity at the amino acid level. <italic>NPF2.5</italic> is predominantly expressed in root cortical cells and its transcription is induced by salt. Functional characterisation of NPF2.5 via its heterologous expression in yeast (<italic>Saccharomyces cerevisiae</italic>) and <italic>Xenopus laevis</italic> oocytes indicated that NPF2.5 is likely to encode a Cl<sup>−</sup> permeable transporter. Arabidopsis <italic>npf2.5</italic> T-DNA knockout mutant plants exhibited a significantly lower Cl<sup>−</sup> efflux from roots, and a greater Cl<sup>−</sup> accumulation in shoots compared to salt-treated Col-0 wild-type plants. At the same time, <inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mn>3</mml:mn><mml:mo>−</mml:mo></mml:msubsup></mml:mrow></mml:math></inline-formula> content in the shoot remained unaffected. Accumulation of Cl<sup>−</sup> in the shoot increased following (1) amiRNA-induced knockdown of <italic>NPF2.5</italic> transcript abundance in the root, and (2) constitutive over-expression of <italic>NPF2.5</italic>. We suggest that both these findings are consistent with a role for NPF2.5 in modulating Cl<sup>−</sup> transport. Based on these results, we propose that NPF2.5 functions as a pathway for Cl<sup>−</sup> efflux from the root, contributing to exclusion of Cl<sup>−</sup> from the shoot of Arabidopsis.</p>