Rice OsYSL15 Is an Iron-regulated Iron(III)-Deoxymugineic Acid Transporter Expressed in the Roots and Is Essential for Iron Uptake in Early Growth of the Seedlings

Abstract

Graminaceous plants take up iron through YS1 (yellow stripe 1) and YS1-like (YSL) transporters using iron-chelating compounds known as mugineic acid family phytosiderophores. We examined the expression of 18 rice (Oryza sativa L.) YSL genes (OsYSL1-18) in the epidermis/exodermis, cortex, and stele of rice roots. Expression of OsYSL15 in root epidermis and stele was induced by iron deficiency and showed daily fluctuation. OsYSL15 restored a yeast mutant defective in iron uptake when supplied with iron(III)-deoxymugineic acid and transported iron(III)-deoxymugineic acid in Xenopus laevisoocytes. An OsYSL15-green fluorescent protein fusion was localized to the plasma membrane when transiently expressed in onion epidermal cells. OsYSL15 promoter-␤-glucuronidase analysis revealed that OsYSL15 expression in roots was dominant in the epidermis/exodermis and phloem cells under conditions of iron deficiency and was detected only in phloem under iron sufficiency. These results strongly suggest that OsYSL15 is the dominant iron(III)-deoxymugineic acid transporter responsible for iron uptake from the rhizosphere and is also responsible for phloem transport of iron. OsYSL15 was also expressed in flowers, developing seeds, and in the embryonic scutellar epithelial cells during seed germination. OsYSL15 knockdown seedlings showed severe arrest in germination and early growth and were rescued by high iron supply. These results demonstrate that rice OsYSL15 plays a crucial role in iron homeostasis during the early stages of growth.

Activation of Rice nicotianamine synthase 2 (OsNAS2) Enhances Iron Availability for Biofortification

“…4A-4C). These genes are membrane transporters responsible for Fe-uptake from soil (Inoue et al, 2009;Ishimaru et al, 2006;Lee et al, 2009a). Expression of OsYSL2, which functions as an Fe(II)-NA transporter important for Fetranslocation (Ishimaru et al, 2010), was also increased in transgenic roots relative to the WT (Fig.…”

“…4). Transcript levels of OsIRT1, OsIRT2 (Ishimaru et al, 2006), and OsYSL15 (Inoue et al, 2009;Lee et al, 2009a) were significantly higher in transgenic roots (Figs. 4A-4C).…”

Iron Uptake and Loading into Rice Grains

“…In barley, MAs are secreted in a diurnal fashion (Takagi et al 1984). The diurnal secretion of MAs has not been fully characterized in rice, although the expression of MA family genes is believed to change in a diurnal fashion (Nozoye et al 2004;Inoue et al 2009). …”

Iron-Binding E3 Ligase Mediates Iron Response in Plants by Targeting Basic Helix-Loop-Helix Transcription Factors

“…Under low-iron conditions, grasses such as rice (Oryza sativa) and maize (Zea mays) primarily utilize the Strategy II response, whereby they release phytosiderophores into the rhizosphere that bind to ferric iron with high affinity. Phytosiderophore-ferric iron complexes are transported into the root via membrane-localized yellow stripe and yellow stripe-like (YSL) transporters (Curie et al, 2001;Inoue et al, 2009), although several studies suggest that rice is also able to directly uptake ferrous iron (Ishimaru et al, 2006;Cheng et al, 2007).…”