Abstract
Tobacco has frequently been suggested as a candidate plant species for use in phytoremediation of metal contaminated soil but knowledge on the regulation of its metal-homeostasis is still in the infancy. To identify new tobacco metal transport genes that are involved in Zn homeostasis a bioinformatics study using the tobacco genome information together with expression analysis was performed. Ten new tobacco metal transport genes from the ZIP, NRAMP, MTP, and MRP/ABCC families were identified with expression levels in leaves that were modified by exposure to Zn excess. Following exposure to high Zn there was upregulation of NtZIP11-like, NtNRAMP3, three isoforms of NtMTP2, three MRP/ABCC genes (NtMRP5-like, NtMRP10-like, and NtMRP14 like) and downregulation of NtZIP1-like and NtZIP4. This suggests their involvement in several processes governing the response to Zn-related stress and in the efficiency of Zn accumulation (uptake, sequestration, and redistribution). Further detailed analysis of NtZIP1-like provided evidence that it is localized at the plasma membrane and is involved in Zn but not Fe and Cd transport. NtZIP1-like is expressed in the roots and shoots, and is regulated developmentally and in a tissue-specific manner. It is highly upregulated by Zn deficiency in the leaves and the root basal region but not in the root apical zone (region of maturation and absorption containing root hairs). Thus NtZIP1-like is unlikely to be responsible for Zn uptake by the root apical region but rather in the uptake by root cells within the already mature basal zone. It is downregulated by Zn excess suggesting it is involved in a mechanism to protect the root and leaf cells from accumulating excess Zn.
Highlights
For each gene from A. thaliana used as a query, several tobacco homologous sequences were identified on different scaffolds
Further the selected tobacco scaffolds were screened to identify full putative genomic sequences of NtZIP, NtNRAMP, NtMTP, and NtMRP (ABCC) genes, including transcription start sites, exons, introns, and polyadenylation sites using the FGENESH tool (Salamov and Solovyev, 2000), whereas Phobius system based on a hidden Markov model (HMM) approach, was applied to predict membrane topology of NtZIP1-like protein
The bioinformatics analysis using information from the tobacco genome and the detailed expression study has led to the identification of ten new tobacco putative transporters involved in the regulation of Zn accumulation in tobacco leaves
Summary
To improve its capacity to take up and store metals in shoots, it has been transformed with a number of metal homeostasis genes, but with limited success (Gisbert et al, 2003; Martínez et al, 2006; Gorinova et al, 2007; Wojas et al, 2008, 2009; Korenkov et al, 2009; Siemianowski et al, 2011; Barabasz et al, 2013; Wang et al, 2015). NtZIP1-Like in Tobacco Zn Homeostasis part of the resulting phenotype was due to the modulation of endogenous gene expression (Barabasz et al, 2016; Kendziorek et al, 2016). Maintaining high Zn in the above ground organs depends on three major processes operating efficiently: Zn uptake from the soil, root-to-shoot translocation and storage in leaves without detrimental toxic effects
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