Mediation of Zinc and Iron Accumulation in Maize by ZmIRT2, a Novel Iron-Regulated Transporter

Iron (Fe) is an essential micronutrient for plant growth. Iron-regulated transporters (IRTs) play important roles in Fe2+ uptake and transport in strategy I plants. Maize (Zea mays) belongs to a strategy II plant, in which mugineic acid (MA)-Fe3+ uptake is mainly carried out by Yellow Stripe 1 (YS1). However, ZmIRT1 was previously identified by our laboratory. In this study, we isolated a novel gene from maize (ZmIRT2), which is highly homologous to OsIRT2 and ZmIRT1. ZmIRT2 was expressed in roots and anther and was induced by Fe and zinc (Zn) deficiencies. ZmIRT2-GFP fusion protein localized to the plasma membrane and endoplasmic reticulum. ZmIRT2 reversed growth defects involving Zn and Fe uptake in mutant yeast. ZmIRT2 overexpression in maize led to elevated Zn and Fe levels in roots, shoots and seeds of transgenic plants. Transcript levels of ZmIRT1 were elevated in roots, while levels of YS1 were reduced in shoots of ZmIRT2 transgenic plants. Our results imply that ZmIRT2 may function solely with ZmIRT1 to mediate Fe uptake in roots. ZmIRT1, ZmIRT2 and ZmYS1 may function in a cooperative manner to maintain Zn and Fe homeostasis in ZmIRT2 overexpressing plants. Furthermore, ZmIRT2 could be used in fortification efforts to elevate Zn and Fe levels in crop plants.