Planta

, Volume 212, Issue 5, pp 864-871

First online:

In vivo evidence that Ids3 from Hordeum vulgare encodes a dioxygenase that converts 2′-deoxymugineic acid to mugineic acid in transgenic rice

  • Takanori KobayashiAffiliated withLaboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
  • , Hiromi NakanishiAffiliated withLaboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
  • , Michiko TakahashiAffiliated withCore Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation, 2-1-6 Sengen, Tsukuba 305-0047, Japan
  • , Shinji KawasakiAffiliated withNational Institute of Agrobiological Resources, 2-1-2 Kan'non-dai, Tsukuba 305-8602, Japan
  • , Naoko-Kishi NishizawaAffiliated withLaboratory of Plant Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
  • , Satoshi MoriAffiliated withLaboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan

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Abstract.

We proposed that an Fe-deficiency-induced gene, Ids3 (Iron deficiency specific clone no. 3), from barley (Hordeum vulgare L.) roots encodes a dioxygenase that catalyzes the hydroxylation step from 2′-deoxymugineic acid (DMA) to mugineic acid (MA). To prove this hypothesis, we introduced the Ids3 gene into rice (Oryza sativa L.), which lacks Ids3 homologues and secretes DMA, but not MA. Transgenic rice plants, carrying either Ids3 cDNA or a barley genomic DNA fragment (20 kb) containing Ids3, were obtained using Agrobacterium-mediated transformation. Ids3 cDNA under the control of the cauliflower mosaic virus 35S promoter was constitutively expressed in both the roots and the leaves of the transgenic rice, regardless of Fe nutrition status. In contrast, in the roots of transformants carrying a barley genomic fragment, transcripts of Ids3 were markedly increased in response to Fe deficiency. Slight expression of Ids3 was also observed in the leaves of the Fe-deficient plants. Western blot analysis confirmed the induction of Ids3 in response to Fe deficiency in the roots of the transformants carrying a genomic fragment. These expression patterns indicate that the 5′-flanking region of Ids3 works as a strong Fe-deficiency-inducible promoter in rice, as well as in barley. Both kinds of transgenic rice secreted MA in addition to DMA under Fe-deficient conditions, but wild-type rice secreted only DMA. This is in vivo evidence that IDS3 is the “MA synthase” that converts DMA to MA.

Key words: Dioxygenase Iron deficiency Mugineic acid family phytosiderophores Mugineic acid synthase Oryza (transgenic) Transgenic rice