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ARS Home » Northeast Area » Ithaca, New York » Robert W. Holley Center for Agriculture & Health » Plant, Soil and Nutrition Research » Research » Publications at this Location » Publication #319904
Title: Root and shoot transcriptome analysis of two ecotypes of Noccaea caerulescens uncovers the role of NcNramp1 in Cd hyperaccumulation

Author
item MILNER, MATTHEW - Cornell University
item MITANI-UENO, NAMIKI - Okayama University
item YAMAJI, NAOKI - Okayama University
item YOKOSHO, KENGO - Okayama University
item Craft, Eric
item FEI, ZHANGJUN - Boyce Thompson Institute
item EBBS, STEPHEN - Southern Illinois University
item MA, JIAN FENG - Okayama University
item Kochian, Leon

Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2014
Publication Date: 2/15/2014
Citation: Milner, M., Mitani-Ueno, N., Yamaji, N., Yokosho, K., Craft, E.J., Fei, Z., Ebbs, S., Ma, J., Kochian, L.V. 2014. Root and shoot transcriptome analysis of two ecotypes of Noccaea caerulescens uncovers the role of NcNramp1 in Cd hyperaccumulation. Plant Journal. 78:398-410.

Interpretive Summary: Heavy metal contamination of soils poses serious problems worldwide, and the current technologies used to remediate soils are costly and disruptive. There is considerable interest in the use of terrestrial plants to clean up heavy metals from the soil. Several metal hyperaccumulating plant species have been identified that tolerate highly contaminated soils and accumulate these metals to high concentrations. We have been studying the mechanisms for metal hyperaccumulation in Noccaea caerulescens, a zinc/cadmium (Zn/Cd) hyperaccumulator. Because Cd is a highly toxic environmental contaminant, we are particularly interested in determining the molecular basis for Cd hyperaccumulation in this plant species. In this study we compared the expression of thousands of genes in Noccaea roots and shots in two different accessions of the plant form different regions of the world. The accession from the south of France, called Ganges, is a much better Cd hyperaccumulator than the accession from Belgium, Prayon, while both accessions hyperaccumulated Zn equally well. In comparing gene expression between the two accessions in response to toxic levels of Cd, we identified a gene encoding a metal transporter from the Nramp family of micronutrient transporters that was much more highly expressed in Ganges. This transporter, which we named NcNramp1, was characterized for its role in Cd hyperaccumulation. We showed it plays a key role in moving the Cd that had been absorbed from the soil into the root, from the root to the shoot, where it is stored and detoxified in leaf cells. We are now studying how the expression of this transporter can be increased in other plant higher biomass plant species to be used for the phytoremediation of Cd contaminated soils.

Technical Abstract: The Zn/Cd hyperaccumulator, Noccaea caerulescens, has been studied extensively for its ability to accumulate Zn and Cd in its leaves to extremely high levels. Previous studies have indicated that the Zn and Cd hyperaccumulation trait exhibited by this species involves different transport and tolerance mechanisms. It has also been well documented that certain ecotypes of N. caerulescens, especially ecotypes from the south of France such as Ganges, are much better Cd hyperaccumulators than ecotypes such as Prayon. However, there does not seem to be much ecotypic variation for Zn hyperaccumulation in N. caerulescens. In this study we employed a comparative transcriptomics approach to look at root and shoot gene expression in Ganges and Prayon seedlings in response to Cd stress to identify transporter genes that were more highly expressed in either the roots or shoots of the superior Cd accumulator, Ganges. Comparison of the transcriptomes from the two ecotypes of Noccaea caerulescens identified a number of genes encoding metal transporters that were more highly expressed in the Ganges ecotype in response to Cd stress. Characterization of one of these transporters, NcNramp1, showed that it is involved in the influx of Cd across the endodermal plasma membrane and thus may play a key role in Cd flux into the stele and root-to-shoot Cd transport. NcNramp1 may be one of the main transporters involved in Cd hyperaccumulation in N. caerulescens and genome copy number appears to be the main reason for high NcNramp1 gene expression underlying the increased Cd accumulation in the Ganges ecotype relative to Prayon.