Abstract
The zinc-regulated transporters, iron-regulated transporter-like proteins (ZIPs), the natural resistance and macrophage proteins (NRAMP), the heavy metal ATPases (HMAs) and the metal tolerance or transporter proteins (MTPs) families are involved in cadmium (Cd) uptake, translocation and sequestration in plants. Mulberry (Morus L.), one of the most ecologically and economically important (as a food plant for silkworm production) genera of perennial trees, exhibits excellent potential for remediating Cd-contaminated soils. However, there is no detailed information about the genes involved in Cd2+ transport in mulberry. In this study, we identified 31 genes based on a genome-wide analysis of the Morus notabilis genome database. According to bioinformatics analysis, the four transporter gene families in Morus were distributed in each group of the phylogenetic tree, and the gene exon/intron structure and protein motif structure were similar among members of the same group. Subcellular localization software predicted that these transporters were mainly distributed in the plasma membrane and the vacuolar membrane, with members of the same group exhibiting similar subcellular locations. Most of the gene promoters contained abiotic stress-related cis-elements. The expression patterns of these genes in different organs were determined, and the patterns identified, allowing the categorization of these genes into four groups. Under low or high-Cd2+ concentrations (30 μM or 100 μM, respectively), the transcriptional regulation of the 31 genes in root, stem and leaf tissues of M. alba seedlings differed with regard to tissue and time of peak expression. Heterologous expression of MaNRAMP1, MaHMA3, MaZIP4, and MaIRT1 in Saccharomyces cerevisiae increased the sensitivity of yeast to Cd, suggested that these transporters had Cd transport activity. Subcellular localization experiment showed that the four transporters were localized to the plasma membrane of yeast and tobacco. These results provide the basis for further understanding of the Cd tolerance mechanism in Morus, which can be exploited in Cd phytoremediation.
Highlights
Due to increasing industrial demands, global cadmium (Cd) extraction from mining increased overall by 19.1% between 2000 and 2016
To further understand the mechanisms of Cd-phytoremediation, and to screen for key genes related to Cd uptake, translocation and sequestration in Morus, we identified nine ZIPs, four natural resistance and macrophage proteins (NRAMP), 8 heavy metal ATPases (HMAs) and 10 metal tolerance or transporter proteins (MTPs) (31 genes in total) from M. notabilis
Hidden Markov model (HMM) profiles (PF02535, PF01566, and PF01545) for domains corresponding to ZIP, NRAMP, and MTP gene families were downloaded from Pfam database1
Summary
Due to increasing industrial demands, global cadmium (Cd) extraction from mining increased overall by 19.1% between 2000 and 2016. In 2016, mine production of recoverable Cd was 23000 tons, with China and Korea being the major producers of Cd, with 7400 and 4500 tons of Cd production, respectively (USGS, 2017). Chronic human exposure to Cd at high concentrations (>30 μg·d−1) has the potential to cause kidney damage, bone lesions (itai–itai disease), cancer and lung insufficiency (Figueroa, 2008; Gad, 2014). The main route of human exposure to Cd is through the diet, due to soil Cd pollution (Clemens et al, 2013). A number of Cd-contaminated soil remediation techniques have been researched; compared with many physical and chemical approaches to this problem, phytoremediation is a more environmentally friendly and costeffective method (Raskin et al, 1997)
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