Arabidopsis Yellow Stripe‐Like2 (YSL2): a metal‐regulated gene encoding a plasma membrane transporter of nicotianamine–metal complexes

Abstract

SummaryThe Yellow Stripe-Like (YSL) family of proteins has been identified based on sequence similarity to maize Yellow Stripe1 (YS1), the transporter responsible for the primary uptake of iron from the soil. YS1 transports iron that is complexed by specific plant-derived Fe(III) chelators called phytosiderophores (PS). Non-grass species of plants neither make nor use PS, yet YSL family members are found in non-grass species (monocot, dicot, gymnosperm, and moss species) including Arabidopsis thaliana. YSLs in non-grasses have been hypothesized to transport metals complexed by nicotianamine (NA), an iron chelator that is structurally similar to PS and which is found in all higher plants. Here we show that Arabidopsis YSL2 (At5g24380) transports iron and copper when these metals are chelated by NA. YSL2 is expressed in many cell types in both roots and shoots, suggesting that diverse cell types obtain metals as metal-NA complexes. YSL2 transcription is regulated by the levels of iron and copper in the growth medium. Based on its expression pattern, a major function of the YSL2 appears to be in the lateral movement of metals in the vasculature.

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

“…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). To our knowledge, cell type-specific expression of NA synthases has not been shown directly in Arabidopsis.…”

Nicotianamine Functions in the Phloem-Based Transport of Iron to Sink Organs, in Pollen Development and Pollen Tube Growth in Arabidopsis

“…YSL proteins may act as Fe-NA transporters. YSL1 and YSL2 transporters seem to be active mainly in the xylem parenchyma of the leaf veins but not the phloem cells themselves (DiDonato et al, 2004;Le Jean et al, 2005;Schaaf et al, 2005;Waters et al, 2006). YSL3 promoter activity was detected throughout the parenchyma of veins but not in xylem or phloem (Waters et al, 2006).…”

“…Short-distance translocation of NA across membranes is achieved through the activities of various transport proteins that may transport free NA (Haydon et al, 2012) or metal-NA chelates, the latter of which includes certain members of the YELLOW STRIPE1-LIKE (YSL) oligopeptide transporter family (Curie et al, 2001. Arabidopsis thaliana YSL1, YSL2, and YSL3 are expressed in vascular bundles and are induced by Fe (DiDonato et al, 2004;Schaaf et al, 2005). These YSL transporters presumably mediate the lateral movement of Fe-NA from the xylem and phloem and are involved in reproduction and seed Fe loading (Le Jean et al, 2005;Waters et al, 2006;Chu et al, 2010).…”

A Comparative Inventory of Metal Transporters in the Green Alga Chlamydomonas reinhardtii and the Red Alga Cyanidioschizon merolae

“…Phytosiderophores are not synthesized in Arabidopsis, a strategy I species, but eight YS1 homologs (AtYSL1-8) are found in the plant genome. The AtYSL2 protein has been shown to transport iron and copper chelated by nicotianamine, a precursor of phytosiderophores (DiDonato et al, 2004).…”