Different roles of Arabidopsis NIP3;1 and NIP1;1 in root-to-shoot and root-tip distributions of arsenite
Wenzhong Xu, Wentao Dai, Hongling Shen, Sheng Li, Yangyang Sun, Yanshan Chen, Huili Yan, Hua Xu, Zhenyan He, Mi Ma^*

Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing 100093.
^*Corresponding Author：Tel: (+8610) 62836255; Fax: (+8610)62836690; E-mail: mami@ibcas.ac.cn

Abstract
In Arabidopsis, the roles of the NIPs in the arsenite distribution in plants remain poorly understood. Here, we report that Arabidopsis NIP3;1 and NIP1;1 play different major roles in the shoot and root distributions of arsenite. The nip3;1 loss-of-function mutants displayed obvious improvements in high arsenite tolerance for aboveground growth, which was different from the tolerance to arsenite of the primary root growth of nip1;1. The shoots of nip3;1 accumulated less As than did those of the wild type under high arsenite conditions, indicating that NIP3;1 is involved in arsenite uptake and root-to-shoot translocation. Studies with NIP1;1-promoter-β-glucuronidase constructs demonstrated that NIP1;1 was expressed in the whole root, particularly in the root-tip zone, and that the first exon/intron region was required for strong and specific expression of NIP1;1 in root-tip cells. A knockout mutation of NIP1;1 reduced arsenic accumulation in the root tips under arsenite conditions, suggesting that NIP1;1 plays a key role in the arsenite distribution at root-tip cells. Additionally, a nip3;1 nip1;1-double-mutant had a phenotype with strong arsenite tolerance that showed improved growth of both roots and shoots under arsenite conditions. Taken together, we propose that NIP3;1 and NIP1;1 function as arsenite transporters for root-to-shoot translocation and root-tip distribution, respectively, in Arabidopsis.

Key words: Arabidopsis; arsenite; NIP1;1; NIP3;1; root-tip distribution; root-to-shoot translocation