Yellow Stripe1. Expanded Roles for the Maize Iron-Phytosiderophore Transporter

Abstract

Graminaceous monocots, including most of the world's staple grains (i.e. rice, corn, and wheat) use a chelation strategy (Strategy II) for primary acquisition of iron from the soil. Strategy II plants secrete phytosiderophores (PS), compounds of the mugineic acid family that form stable Fe(III) chelates in soil. Uptake of iron-PS chelates, which occurs through specific transporters at the root surface, thus represents the primary route of iron entry into Strategy II plants. The gene Yellow stripe1 (Ys1) encodes the Fe(III)-PS transporter of maize (Zea mays). Here the physiological functions performed by maize YS1 were further defined by examining the pattern of Ys1 mRNA and protein accumulation and by defining YS1 transport specificity in detail. YS1 is able to translocate iron that is bound either by PS or by the related compound, nicotianamine; thus, the role of YS1 may be to transport either of these complexes. Ys1 expression at both the mRNA and protein levels responds rapidly to changes in iron availability but is not strongly affected by limitation of copper or zinc. Our data provide no support for the idea that YS1 is a transporter of zinc-PS, based on YS1 biochemical activity and Ys1 mRNA expression patterns in response to zinc deficiency. YS1 is capable of transporting copper-PS, but expression data suggest that the copper-PS uptake has limited significance in primary uptake of copper.

Mutations in Arabidopsis Yellow Stripe-Like1 and Yellow Stripe-Like3 Reveal Their Roles in Metal Ion Homeostasis and Loading of Metal Ions in Seeds

“…NA has been implicated in metal homeostasis in a number of studies using the NA synthesis mutant chln of tomato (Stephan and Grun, 1989;Becker et al, 1992;Ling et al, 1999). Previous work in our lab has demonstrated that the maize YS1 protein transports Fe(II)-NA Roberts et al, 2004). Furthermore, we have characterized AtYSL2 as an Fe(II)-NA and Cu-NA transporter on the basis of complementation of the yeast (Saccharomyces cerevisiae) mutants fet3fet4 and ctr1 (DiDonato et al, 2004), which are unable to grow on Fe-and Cu-limiting media, respectively.…”

“…In previous work, our group has demonstrated that ZmYS1 and AtYSL2 are capable of transporting Fe(II)-NA into cells DiDonato et al, 2004;Roberts et al, 2004), and others have shown that OsYSL2 of rice (Oryza sativa) can transport Fe(II)-NA (Koike et al, 2004). Here, we use a genetic approach to show that the combination of null mutations in two AtYSLs, YSL1 and YSL3, results in a severe phenotype that includes interveinal chlorosis; altered metal concentrations in leaves, roots, and seeds; and greatly decreased fertility.…”

Moving micronutrients from the soil to the seeds: Genes and physiological processes from a biofortification perspective

“…These transporters are the yellow stripe-like (YSL) proteins, which are members of the oligopeptide transport (OPT) family. YellowStripe1 (YS1) is the primary Fe(III)-mugineic acid (phytosiderophore) uptake protein in maize [34] and is also involved in internal translocation of Fe [145,146]. In nongrasses, YSL proteins seem to function in interorgan translocation rather than for primary uptake of iron at the root surface.…”

Role of Iron in Plant Growth and Metabolism

“…YS1 is a proton-coupled symporter of Fe (III)-PS complexes (Schaff et al, 2004). The transport activity and specificity of YS1 transporters from maize (ZmYS1), barley (HvYS1), and rice (OsYSL15) have been examined using yeast growth complementation and radioactive uptake assays in two electrode voltage clamp experiments in Xenopus leavis oocytes (Curie et al, 2001;Roberts et al, 2004;Schaaf et al, 2004;Murata et al, 2006;Inoue et al, 2009;Lee et al, 2009).…”