Rice plants take up iron as an Fe3+-phytosiderophore and as Fe2+.
Only graminaceous monocots possess the Strategy II iron (Fe)-uptake system in which Fe is absorbed by roots as an Fe3+-phytosiderophore. In spite of being a Strategy II plant, however, rice (Oryza sativa) contains the previously identified Fe2+ transporter OsIRT1. In this study, we isolated the OsIRT2 gene from rice, which is highly homologous to OsIRT1. Real-time PCR analysis revealed that OsIRT1 and OsIRT2 are expressed predominantly in roots, and these transporters are induced by low-Fe conditions. When expressed in yeast (Saccharomyces cerevisiae) cells, OsIRT2 cDNA reversed the growth defects of a yeast Fe-uptake mutant. This was similar to the effect of OsIRT1 cDNA. OsIRT1- and OsIRT2-green fluorescent protein fusion proteins localized to the plasma membrane when transiently expressed in onion (Allium cepa L.) epidermal cells. OsIRT1 promoter-GUS analysis revealed that OsIRT1 is expressed in the epidermis and exodermis of the elongating zone and in the inner layer of the cortex of the mature zone of Fe-deficient roots. OsIRT1 expression was also detected in the ccompanion cells. Analysis using the positron-emitting tracer imaging system showed that rice plants are able to take up both an Fe3+-phytosiderophore and Fe2+. This result indicates that, in addition to absorbing an Fe3+-phytosiderophore, rice possesses a novel Fe-uptake system that directly absorbs the Fe2+, a strategy that is advantageous for growth in submerged conditions.
Ishimaru
Yasuhiro
Y
Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Suzuki
Motofumi
M
Tsukamoto
Takashi
T
Suzuki
Kazumasa
K
Nakazono
Mikio
M
Kobayashi
Takanori
T
Wada
Yasuaki
Y
Watanabe
Satoshi
S
Matsuhashi
Shinpei
S
Takahashi
Michiko
M
Nakanishi
Hiromi
H
Mori
Satoshi
S
Nishizawa
Naoko K
NK
D000595:Amino Acid Sequence; D027682:Cation Transport Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D038181:FMN Reductase / Q000235:genetics; D017343:Genes, Plant / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000032:analysis; D007501:Iron / Q000378:metabolism*; D008969:Molecular Sequence Data; D012275:Oryza / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D010940:Plant Proteins / Q000378:metabolism* / Q000502:physiology; D018517:Plant Roots / Q000378:metabolism; D018547:Plant Stems / Q000378:metabolism; D018749:RNA, Plant / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development; D016415:Sequence Alignment; D015854:Up-Regulation
D027682:Cation Transport Proteins; D010940:Plant Proteins; D018749:RNA, Plant; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D007501:Iron; D038181:FMN Reductase; C023903:ferric citrate iron reductase