Nicotianamine is a major player in plant Zn homeostasis

Abstract

Nicotianamine (NA) is among the most studied plant metal chelators. A large body of evidence supports its crucial role for Fe distribution in plants and as a precursor of phytosiderophore synthesis in grasses. NA forms stable complexes in vitro not only with Fe(II) and Fe(III) but also with various other divalent metal cations including Zn(II). Early observations indicated a possible contribution of NA to Zn trafficking in plants. Numerous studies on transgenic monocot and dicot plants with modulated NA levels have since then reported Zn accumulation phenotypes. NAS genes were shown to represent promising targets for biofortification efforts. For instance, NA was found to bind Zn in rice grains in a form bioavailable for humans. Recently, additional strong support for the existence of Zn-NA complexes in planta has been obtained in rice, Arabidopsis thaliana and the Zn hyperaccumulating plant A. halleri. We review the evidence for a role of NA in the intercellular and long-distance transport of Zn in plants and discuss open questions.

Got to hide your Zn away: Molecular control of Zn accumulation and biotechnological applications

“…Nicotianamine and Zn homeostasis seem to be linked in both monocots and dicots, as Zn(II)-nicotianamine complexes are the major Zn form in rice phloem sap and nicotianamine is important for long-distance Zn transport in tobacco plants (for a comprehensive review, see [14]). Nicotianamine has been related to Zn homeostasis in hyperaccumulators and has also been considered a target for biofortification (see Section 3 and 5).…”

“…(I) In A. halleri, Zn chelation by nicotianamine might control xylem loading efficiency and formation of Zn complexes with organic acids such as malate and citrate, which are the main Zn ligands in the xylem [125]. (I) Detoxification of Zn by chelation with NA might contribute to the symplastic mobility of Zn 2+ towards the xylem in A. halleri [14,124]. (I) Histidine can prevent vacuolar metal sequestration in roots of N. caerulescens increasing Zn xylem loading [123].…”

“…In fact, no Zn(II)-nicotianamine transport activity has been observed so far. Still, members of the YSL family are considered the best candidates to mediate Zn(II)-nicotianamine (and Zn(III)-phytosiderophore) transport [12,14]. The identification of specific proteins with these functions could be pursued by extensive mutant yeast complementation assays and/or injection of oocytes with cDNAs from the YSL family, followed by electrophysiology studies, using Zn 2+ complexed with nicotianamine and phytosiderophores as Zn source.…”

“…1) [76]. Nicotianamine has already been related to symplastic Zn movement [14]. The Arabidopsis genome also contains two genes closely related to AtZIF1, named AtZIFL1 and AtZIFL2, but involvement with Zn homeostasis has not been demonstrated for any of them [77].…”

Papel de COPT1, COPT2, MTP2 y ZIP6 en el transporte y la homeostasis de metales en Medicago truncatula

“…Los genes para la síntesis de NA (NAS) se sobreexpresan en condiciones de deficiencia de cobre o zinc (Wintz et al, 2003). De hecho, se relaciona la mayor abundancia de transcritos de NAS en A. halleri con la capacidad de hiperacumular zinc en esta especie respecto a A. thaliana (Clemens et al, 2013;Deinlein et al, 2012). Mientras que en el xilema el principal ligando de hierro parece ser el citrato (Álvarez-Fernández et al, 2010;Rellán-Álvarez et al, 2014), el principal ligando propuesto en el transporte de zinc y cobre tanto por xilema como por floema sería NA (Haydon et al, 2012;Rellán-Álvarez et al, 2008;von Wirén et al, 1999).…”