Characterization of Poplar ZIP Family Members ZIP1.2 and ZNT1
Regulation of a heavy metal such as zinc (Zn) throughout a plant has been attributed to the Zn transporter gene ZNT1 and other members of the larger ZIP transporter family. However, genes have not been characterized in a high-biomass, perennial, woody species, such as poplar (Populus trichocarpa). The poplar genome was searched for ZIP transporter members and analyzed via a phylogenetic analysis. Afterwards, two of these genes were selected for further characterization via transcriptional analysis. Poplar appears to contain 13 genes with sequence orthology to ZIP family members. Of these 13 genes, only one gene appears to be a close ortholog to the TcZNT1 gene in the hyperaccumulating Thlaspi caerulescens (syn. Noccaea caerulescens). Transcript abundance of this poplar ortholog, PtZNT1, and another ZIP poplar member, PtZIP1.2, generally decreased in stem and root tissue, respectively, as levels of Zn increase in poplar. Furthermore, PtZNT1 promoter abundance does not localize to a specific tissue nor have the overall promoter abundance of TcZNT1 which localizes in vascular tissue. PtZNT1 promoter abundance is stable and active across tissues but at an overall lower level than the hyperaccumulator. These characterizations of ZIP members in poplar may indicate a specifically evolved coordination of tissue specific Zn transporters for regulation of nutrients.