Abstract
SummaryMany metal transporters in plants are promiscuous, accommodating multiple divalent cations including some which are toxic to humans. Previous attempts to increase the iron (Fe) and zinc (Zn) content of rice endosperm by overexpressing different metal transporters have therefore led unintentionally to the accumulation of copper (Cu), manganese (Mn) and cadmium (Cd). Unlike other metal transporters, barley Yellow Stripe 1 (HvYS1) is specific for Fe. We investigated the mechanistic basis of this preference by constitutively expressing HvYS1 in rice under the control of the maize ubiquitin1 promoter and comparing the mobilization and loading of different metals. Plants expressing HvYS1 showed modest increases in Fe uptake, root‐to‐shoot translocation, seed accumulation and endosperm loading, but without any change in the uptake and root‐to‐shoot translocation of Zn, Mn or Cu, confirming the selective transport of Fe. The concentrations of Zn and Mn in the endosperm did not differ significantly between the wild‐type and HvYS1 lines, but the transgenic endosperm contained significantly lower concentrations of Cu. Furthermore, the transgenic lines showed a significantly reduced Cd uptake, root‐to‐shoot translocation and accumulation in the seeds. The underlying mechanism of metal uptake and translocation reflects the down‐regulation of promiscuous endogenous metal transporters revealing an internal feedback mechanism that limits seed loading with Fe. This promotes the preferential mobilization and loading of Fe, therefore displacing Cu and Cd in the seed.
Highlights
Iron (Fe) is an important micronutrient for all living organisms (Winterbourn, 1995)
Metal acquisition and mobilization in plants are controlled by several families of membrane-bound metal transporters (Hall and Williams, 2003; Vert et al, 2002) including the Fe-regulated transporter (IRT), natural resistance-associated macrophage protein (NRAMP), cation diffusion facilitator (CDF), yellow stripe-like (YSL) and heavy metal ATPase (HMA) transporter families, as well as other Fe transporters in the chloroplast and vacuolar membranes (Duy et al, 2007; Hall and Williams, 2003; Vert et al, 2002; Zhang et al, 2012)
We co-transformed 7-day-old mature seed-derived zygotic rice embryos with a plasmid containing HvYS1 driven by the constitutive maize ubiquitin 1 promoter and another plasmid carrying the selectable marker hpt driven by the CaMV35S promoter and regenerated transgenic plants under hygromycin selection
Summary
Iron (Fe) is an important micronutrient for all living organisms (Winterbourn, 1995). In strategy I, Fe2+ ions are taken up into the root epidermis by OsIRT1/OsIRT2 in the plasma membrane (Ishimaru et al, 2006; Lee and An, 2009; Vert et al, 2002) and are transported via the phloem and xylem to accumulate in the seeds (Ishimaru et al, 2010; Takahashi et al, 2011). The DMA-Fe3+ complex is transported through the phloem by YSL18 and accumulates in the seeds in the same form (Ayoma et al, 2009), whereas translocation through the xylem is mediated by the citrate efflux transporter FRDL1 (Yokosho et al, 2009)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
