Arabidopsis NPCC6/NaKR1 is a phloem mobile metal binding protein necessary for phloem function and root meristem maintenance

Hui Tian, Ivan R. Baxter, Brett Lahner, Anke Reinders, David E. Salt, John M. Ward

Research output: Contribution to journalArticle

36 Scopus citations

Abstract

SODIUM POTASSIUM ROOT DEFECTIVE1 (NaKR1; previously called NPCC6) encodes a soluble metal binding protein that is specifically expressed in companion cells of the phloem. The nakr1-1 mutant phenotype includes high Na+, K+, Rb+, and starch accumulation in leaves, short roots, late flowering, and decreased long-distance transport of sucrose. Using traditional and DNA microarray-based deletion mapping, a 7-bp deletion was found in an exon of NaKR1 that introduced a premature stop codon. The mutant phenotypes were complemented by transformation with the native gene or NaKR1-GFP (green fluorescent protein) and NaKR1-β-glucuronidase fusions driven by the native promoter. NAKR1-GFP was mobile in the phloem; it moved from companion cells into sieve elements and into a previously undiscovered symplasmic domain in the root meristem. Grafting experiments revealed that the high Na+ accumulation was due mainly to loss of NaKR1 function in the leaves. This supports a role for the phloem in recirculating Na+ to the roots to limit Na+ accumulation in leaves. The onset of root phenotypes coincided with NaKR1 expression after germination. The nakr1-1 short root phenotype was due primarily to a decreased cell division rate in the root meristem, indicating a role in root meristem maintenance for NaKR1 expression in the phloem.

Original languageEnglish (US)
Pages (from-to)3963-3979
Number of pages17
JournalPlant Cell
Volume22
Issue number12
DOIs
StatePublished - Dec 2010

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