GENOMIC APPROACHES TO IMPROVING TRANSPORT AND DETOXIFICATION OF SELECTED MINERAL ELEMENTS IN CROP PLANTS
Location: Plant, Soil and Nutrition Research
Title: Transport properties for members of the ZIP family in plants and their role in Zn and Mn homeostasis
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 8, 2012
Publication Date: January 3, 2013
Citation: Milner, M., Seamon, J., Kochian, L.V. 2013. Transport properties for members of the ZIP family in plants and their role in Zn and Mn homeostasis. Journal of Experimental Botany. 64(1):369-381.
Interpretive Summary: Plant acquisition of micronutrients such as zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu) from the soil is a complex process, as these metals are usually bound tightly to soil particles and plants have evolved elegant mechanisms for acquiring them. Furthermore, as these metals are very reactive, they can also be toxic heavy metals if accumulated to high levels in organisms. Thus micronutrient metal acquisition is highly regulated. The ZIP family of micronutrient metal transporters are a large gene family in yeast, plants, animals, and humans. In the model plant Arabidopsis, there are 14 ZIP family members, of which only three have been well characterized. In this investigation, we expressed the 11 heretofore uncharacterized Arabidopsis ZIP transporters in yeast mutants defective in Zn, Fe, Cu or Mn uptake to determine what micronutrients these ZIPs can transport. We found that a number of these 11 ZIPs (six) could mediate Zn or Mn uptake. Thus we then focused on two of these ZIPs, AtZIP1 and AtZIP2, for their role in Zn and Mn acquisition and transport in Arabidopsis. We found that both transporters function primarily in Mn transport, specifically in helping mediate Mn translocation from the root to shoot. Mn transport, homeostasis and nutrition is very poorly understood in plants and these findings will help us better understand how plants acquire this metal that is essential for function of all plants.
A better understanding of the role of the Arabidopsis ZIP family of micronutrient transporters is necessary in order to advance our understanding of plant Zn, Fe, Mn and Cu homeostasis. In the current study, the eleven Arabidopsis ZIP family members not yet well characterized were studied for their ability to complement four yeast mutants defective in Zn, Fe, Mn, or Cu uptake. Six Arabidopsis ZIP genes complemented a yeast Zn uptake deficient mutant, one was able to partially complement a yeast Fe uptake deficient mutant, six ZIP family members complemented a Mn uptake deficient mutant, and none complemented the Cu uptake deficient mutant. We then focused on AtZIP1 and AtZIP2 and their possible role(s) in Zn and Mn nutrition. In yeast, AtZIP1 and AtZIP2 both complemented the Zn and Mn uptake mutants, suggesting they both may transport Zn and/or Mn. Expression of both genes is localized to the root stele, and AtZIP1 expression was also found in the leaf vasculature. We also found that AtZIP1 is a vacuolar transporter, while AtZIP2 is localized to the plasma membrane. Functional studies with Arabidopsis AtZIP1 and AtZIP2 T-DNA knockout lines suggest that both transporters play a role in Mn (and possibly Zn) translocation from the root to shoot. AtZIP1 may play a role in remobilizing Mn from the vacuole to cytoplasm for radial movement to the xylem. AtZIP2 on the other hand, may mediate Mn (and possibly Zn) uptake into cells surrounding the root vasculature, for subsequent loading into the xylem.