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Pure Appl. Chem., 2008, Vol. 80, No. 12, pp. 2689-2697

Specific transporter for iron(III): Phytosiderophore complex involved in iron uptake by barley roots

Yoshiko Murata1, Emiko Harada1, Kenji Sugase1, Kosuke Namba1, Manabu Horikawa1, Jian Feng Ma2, Naoki Yamaji2, Daisei Ueno2, Kyosuke Nomoto3, Takashi Iwashita1 and Shoichi Kusumoto1

1 Suntory Institute for Bioorganic Research, 1-1-1 Wakayamadai, Shimamoto-cho, Mishima-gun, Osaka, 618-8503, Japan
2 Research Institute for Bioresources, Okayama University Chuo 2-20-1, Kurashiki 710-0046, Japan
3 Nara Collaboration of Regional Entities for the Advancement of Technological Excellence, 88 Shijyo, Kashihara, Nara 634-0813, Japan

Abstract: Iron (Fe) is an essential element for plant growth. Gramineous plants have generally developed a distinct strategy to efficiently acquire insoluble Fe, which is characterized by the synthesis and secretion of an Fe-chelating substance, phytosiderophore (PS) such as mugineic acid (MA), and by a specific uptake system for Fe(III)-PS complexes. In a previous study, we identified a gene specifically encoding an Fe(III)-PS transporter (HvYS1) in barley. This gene as well as the encoded protein is specifically expressed in the epidermal cells of the roots, and gene expression is greatly enhanced under Fe-deficient conditions. The localization and substrate specificity of HvYS1 indicate that it is a specific transporter in barley roots. In contrast, ZmYS1, which has been reported as an Fe-PS transporter from maize, possesses broad substrate specificity despite a high homology with HvYS1. By assessing the transport activity of a series of HvYS1-ZmYS1 chimeras, we revealed that the outer membrane loop between the 6th and 7th transmembrane regions is essential for the substrate specificity. We also achieved an efficient short-step synthesis of MA and 2'-deoxymugineic acid (DMA). Our new synthetic method enabled us to use them in a large quantity for biological studies.