Overexpression of ZmIRT1 and ZmZIP3 Enhances Iron and Zinc Accumulation in Transgenic Arabidopsis

Abstract

Iron and zinc are important micronutrients for both the growth and nutrient availability of crop plants, and their absorption is tightly controlled by a metal uptake system. Zinc-regulated transporters, iron-regulated transporter-like proteins (ZIP), is considered an essential metal transporter for the acquisition of Fe and Zn in graminaceous plants. Several ZIPs have been identified in maize, although their physiological function remains unclear. In this report, ZmIRT1 was shown to be specifically expressed in silk and embryo, whereas ZmZIP3 was a leaf-specific gene. Both ZmIRT1 and ZmZIP3 were shown to be localized to the plasma membrane and endoplasmic reticulum. In addition, transgenic Arabidopsis plants overexpressing ZmIRT1 or ZmZIP3 were generated, and the metal contents in various tissues of transgenic and wild-type plants were examined based on ICP-OES and Zinpyr-1 staining. The Fe and Zn concentration increased in roots and seeds of ZmIRT1-overexpressing plants, while the Fe content in shoots decreased. Overexpressing ZmZIP3 enhanced Zn accumulation in the roots of transgenic plants, while that in shoots was repressed. In addition, the transgenic plants showed altered tolerance to various Fe and Zn conditions compared with wild-type plants. Furthermore, the genes associated with metal uptake were stimulated in ZmIRT1 transgenic plants, while those involved in intra- and inter- cellular translocation were suppressed. In conclusion, ZmIRT1 and ZmZIP3 are functional metal transporters with different ion selectivities. Ectopic overexpression of ZmIRT1 may stimulate endogenous Fe uptake mechanisms, which may facilitate metal uptake and homeostasis. Our results increase our understanding of the functions of ZIP family transporters in maize.

Is there a strategy I iron uptake mechanism in maize?

“…28 Moreover, the divalent cation transporting activity of ZmIRT1 and ZmZIP3 was confirmed in plants, as the levels of Zn and Fe were increased in ZmIRT1-and ZmZIP3-overexpressing Arabidopsis. 29 Although there is a lack of evidence regarding whether the strategy I system is intact in maize, several genes encoding transcription factors, plasma membrane H C ATPase, and ferric reductases that participate in strategy I were identified in the maize genome. As shown in Table 1, the putative maize orthologs of FIT, H C ATPase (MHA), and FRO were identified by BLAST searches using Arabidopsis genes as queries.…”

Prospecting for Microelement Function and Biosafety Assessment of Transgenic Cereal Plants

“…In addition, transgenic barley overexpressing Arabidopsis zinc transporter AtZIP1 revealed increases in both zinc and iron contents in seeds (Ramesh et al, 2004 ). ZmZIP3 was introduced into Arabidopsis, leading to increased Zn concentration in roots but a decrease in shoots (Li et al, 2015 ). Ferritin protein is also found to take part in the accumulation of Zn in addition to Fe (Vasconcelos et al, 2003 ; Paul et al, 2012 ; Liu et al, 2016 ).…”

Finger on the Pulse: Pumping Iron into Chickpea

“…Whether a similar occurrence may be found in other species remains to be seen, though orthologs of genes associated with Strategy I have also been found in other graminaceous species. An example of this is ZmIRT1 from maize, which was purported to be involved in both uptake and translocation, particularly to the seeds (Li et al, 2015 ). It should be noted that while differences between both strategies primarily affect the uptake process, the involvement of molecular components in the translocation process has further implications for the overall physiology of the plant.…”

“…In Arabidopsis overexpressing AtIRT1 or AtFRO2, no increase in root reduction or protein levels was observed under iron-sufficient conditions due to post-transcriptional regulation (Connolly et al, 2002 , 2003 ). However, no such impediment was noted when the maize homolog, ZmIRT1, was overexpressed, with transgenic lines having significantly higher seed iron contents compared to the wild-type (Li et al, 2015 ). This discrepancy was attributed to the low homology between the ZmIRT1 and the native IRT genes, which may in turn point to a means of bypassing post-transcriptional regulation.…”