Submitted to: Journal of Plant Genetics and Transgenetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2012
Publication Date: 2/5/2012
Publication URL: http://handle.nal.usda.gov/10113/54325
Citation: Adams, J.P., Adeli, A., Hsu, C., Harkess, R., Page, G., Depamphilis, C., Jiao, Y., Schultz, E., Yuccer, C. 2012. Characterization of poplar ZIP family members ZIP1.2 and ZNT1. Journal of Plant Genetics and Transgenetics. 3:1-13. Interpretive Summary: Plants use a variety of transport proteins to regulate interaction with heavy metals, ensuring adequate availability without the toxicity incurred from excesses. One essential heavy metal required for many plant processes is zinc (Zn). However, a critical balance between metal absorbance and tolerance must be regulated as excesses can cause damage due to competition with other essential elements such as iron (Fe), copper (Cu), and calcium (Ca) directly disrupting DNA. Species have evolved varying strategies to maintain this delicate balance. In some species such as Chinese cabbage (Brassica rapa), 200 mg kg-1 Zn acting as a lethal threshold, however, Thlaspi caerulescens can withstand up 30,000 mg kg-1 Zn. Interestingly, all these species have a similar complement of heavy metal related genes regulating interaction with Zn and other essential metals. This regulation involves transport proteins such as the zinc transporter (ZNT), heavy metal ATPase (HMA). ZNT is the member of a much larger Zrt (Zinc Regulated Transporter) like Protein (ZIP) family which play essential roles in the regulation of Zn. The characterization of these specific genes regulating plant-heavy metal interactions has been mostly relegated to small, annual species which are not adequate for large scale remediation. The characterization of these specific genes regulating plant-heavy metal interactions on high-biomass, perennial species such as poplar (Populus trichocarpa) which could potentially be used for bioremediation has not been well documented.
Technical Abstract: A plant must regulate heavy metals to maintain adequate resources for plant processes while protecting against excess metal damage. Regulation of heavy metals such as zinc (Zn) has been attributed to the Zn transporter ZNT1 gene and other members of its larger ZIP transporter family. However, these mechanisms 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 placed in an evolutionary context through phylogenetic analysis. Afterwards, two of these genes were selected for transcriptional analysis. Poplar appears to contain genes with sequence orthology to ZIP family members. Transcript abundance is also indicative of a non-hyperaccumulating phenotype in which PtZIP1 and PtZNT1 decrease as levels of Zn increase. Furthermore, PtZNT1 promoter does not have specific localization in the vascular tissues nor does it have the overall promoter activity of the ZNT gene in the hyperaccumulating Thlaspi caerulescens. Rather, PtZNT1 promoter is stable and active across tissues but at a lower level then the hyperaccumulator. The relationship of these poplar genes with other species, both in genomic compliment and transcript activity, indicates poplar has not faced the evolutionary challenges of hyperaccumulators. Proliferation and conservation of specific gene members, such as ZIP and divergent expression patterns, have contributed to the non-hyperaccumulator, metal regulating phenotype of this perennial species.