Rice plants take up iron as an Fe³⁺‐phytosiderophore and as Fe²⁺

Abstract

SummaryOnly graminaceous monocots possess the Strategy II iron (Fe)-uptake system in which Fe is absorbed by roots as an Fe 3þ -phytosiderophore. In spite of being a Strategy II plant, however, rice (Oryza sativa) contains the previously identified Fe 2þ 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 Fe 3þ -phytosiderophore and Fe 2þ . This result indicates that, in addition to absorbing an Fe 3þ -phytosiderophore, rice possesses a novel Fe-uptake system that directly absorbs the Fe 2þ , a strategy that is advantageous for growth in submerged conditions.

Cell-Type Specificity of the Expression of Os BOR1, a Rice Efflux Boron Transporter Gene, Is Regulated in Response to Boron Availability for Efficient Boron Uptake and Xylem Loading

“…This represents a major difference between Os BOR1 and At BOR1. There are several reports of nutrient transporter genes that are induced by the nutrient conditions, including the rice genes AMT1;2 (Sonoda et al, 2003) and IRT1 (Ishimaru et al, 2006) and the Arabidopsis genes YSL2 (Schaaf et al, 2005) and the AMTs (for review, see Loque and von Wiré n, 2004), but in these cases, no changes in cell-type specific patterns of expression were reported.…”

“…Therefore, it is important to regulate B transport in response to B conditions in the environment, as with other essential nutrients. For example, major transporters in plants, such as the ammonium transporters (AMTs) (Loque and von Wiré n, 2004) and iron transporters (Ishimaru et al, 2006) are regulated at the transcriptional level and respond to the status of the corresponding nutrient. The iron transporter gene At IRT1 is regulated at both transcriptional and posttranscriptional levels (Connolly et al, 2002).…”

Review on iron availability in soil: interaction of Fe minerals, plants, and microbes

“…Under Fe-deficient conditions, PS s secretion into the rhizosphere and biosynthesis of Ps s in plant tissues are markedly increased (Nagasaka et al 2009), with positive effect in the PS s -mediated Femobilization process in the rhizosphere. It is interesting to note that rice, a strategy II plant releasing PS s (2′-deoxymugineic acid [DMA]) and taking up the entire Fe III -PS complexes, is also able to take up directly Fe II from the soil solution, definitely an advantage when rice is cultivated in submerged conditions (Ishimaru et al 2006). On the contrary, it has been recently demonstrated that a Fe III complex with DMA, a PS s released by maize roots, could be absorbed directly by roots of a neighboring dicot using a transporter codified by a gene belonging to the yellow stripe1-like (YSL) family and located at the root epidermis (Xiong et al 2013), representing a valid opportunity in Fe acquisition process of dicots when intercropped with monocots.…”

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).…”