A Novel Barley Yellow Stripe 1-Like Transporter (HvYSL2) Localized to the Root Endodermis Transports Metal-Phytosiderophore Complexes

Recent advances in our understanding of how graminaceous plants take up insoluble forms of iron from the rhizosphere and mobilize them in plant tissues are primarily based on the identification of various transporters that are specific to metal-phytosiderophore (PS) complexes containing mugineic acid and deoxymugineic acid. Barley (Hordeum vulgare L.) yellow stripe 1 (HvYS1) is a metal-PS transporter that preferentially transports Fe(III)-PS compared with other metal complexes. Here, we report the cloning and characterization of HvYSL2, a novel metal-PS transporter encoding gene. HvYSL2 is composed of 702 amino acids with 14 transmembrane domains, which are conserved among this class of transporters, and exhibits 67.3% identity to HvYS1. Electrophysiological experiments with Xenopus laevis oocytes revealed that HvYSL2 transports PS complexes with Fe(III), Zn(II), Ni(II), Cu(II), Mn(II) or Co(II); this constitutes a broader range of substrate preference than HvYS1. Real-time PCR analysis revealed that HvYSL2 mRNA is expressed in shoots and also in roots, where it is induced under iron-deficient conditions. Moreover, immunohistochemistry in roots revealed that HvYSL2 is localized to the endodermis, whereas HvYS1 is expressed primarily in the epidermis. These data suggest that HvYSL2 is spatially distinct from HvYS1 and plays a unique role in delivering a broad range of essential metals in barley.