The Analysis of Arabidopsis Nicotianamine Synthase Mutants Reveals Functions for Nicotianamine in Seed Iron Loading and Iron Deficiency Responses      

Abstract

Nicotianamine chelates and transports micronutrient metal ions in plants. It has been speculated that nicotianamine is involved in seed loading with micronutrients. A tomato (Solanum lycopersicum) mutant (chloronerva) and a tobacco (Nicotiana tabacum) transgenic line have been utilized to analyze the effects of nicotianamine loss. These mutants showed early leaf chlorosis and had sterile flowers. Arabidopsis (Arabidopsis thaliana) has four NICOTIANAMINE SYNTHASE (NAS) genes. We constructed two quadruple nas mutants: one had full loss of NAS function, was sterile, and showed a chloronerva-like phenotype (nas4x-2); another mutant, with intermediate phenotype (nas4x-1), developed chlorotic leaves, which became severe upon transition from the vegetative to the reproductive phase and upon iron (Fe) deficiency. Residual nicotianamine levels were sufficient to sustain the life cycle. Therefore, the nas4x-1 mutant enabled us to study late nicotianamine functions. This mutant had no detectable nicotianamine in rosette leaves of the reproductive stage but low nicotianamine levels in vegetative rosette leaves and seeds. Fe accumulated in the rosette leaves, while less Fe was present in flowers and seeds. Leaves, roots, and flowers showed symptoms of Fe deficiency, whereas leaves also showed signs of sufficient Fe supply, as revealed by molecular-physiological analysis. The mutant was not able to fully mobilize Fe to sustain Fe supply of flowers and seeds in the normal way. Thus, nicotianamine is needed for correct supply of seeds with Fe. These results are fundamental for plant manipulation approaches to modify Fe homeostasis regulation through alterations of NAS genes.

Phloem-Specific Methionine Recycling Fuels Polyamine Biosynthesis in a Sulfur-Dependent Manner and Promotes Flower and Seed Development

“…To assess if the S deficiency-induced reproductive failure of mti1 and dep1 could be caused by a lack of NA, NA and metal concentrations of inflorescences were measured. NA levels were in the same order of magnitude as reported elsewhere (Klatte et al, 2009;WaduwaraJayabahu et al, 2012) and apparently dependent on the supplied sulfate concentration. However, also under the least S concentration supplied, plants were still able to synthesize a minimum of NA.…”

“…Regarding the latter, NA is most important for the phloem mobility of Fe, Zn, and Cu (Klatte et al, 2009;Deinlein et al, 2012;Haydon et al, 2012;Schuler et al, 2012;Zheng et al, 2012). Furthermore, several phloem localized NA transporters have been identified (Koike et al, 2004;Chu et al, 2010;Zheng et al, 2012), some of which appeared to mediate source-to-sink translocation of Fe and other metals during plant senescence (DiDonato et al, 2004).…”

iTRAQ Protein Profile Analysis of Arabidopsis Roots Reveals New Aspects Critical for Iron Homeostasis

“…Increased production of ethylene and nicotianamine (NA), an important micrometal chelator in plant cells that plays a crucial role in Fe homeostasis and transport (Klatte et al, 2009) from SAM and chelation of Fe by citrate during long-distance transport, may be the cause for some of these changes. A comprehensive picture of the metabolic events that are triggered by Fe shortage, however, is still lacking.…”

Optimal copper supply is required for normal plant iron deficiency responses

“…The sensing mechanisms are not known, but the metal chelator nicotianamine is important for Fe homestasis 35,36 and can bind both Fe and Cu. 37 We also showed that under Fe deficiency, plants were strikingly more susceptible to Cu toxicity.…”