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Ramie (Boehmeria nivea) is a perennial herb that is highly tolerant of heavy metals. In the present study, we cloned a novel metallothionein‐like gene from ramie; this gene, termed BnMTL, encodes a putative 46 amino acid protein with a molecular mass of 4.38 kDa. Analysis using quantitative RT‐PCR revealed that cadmium (Cd2+) treatment results in elevated expression of BnMTL in the roots. We heterologously overexpressed BnMTL in Escherichia coli cells to examine its binding to Cd2+ and its possible role in homeostasis. Recombinant E. coli cells expressing BnMTL exhibited a high tolerance of Cd2+ stress up to a concentration of 1 mm, and the observed accumulation of Cd2+ was almost eight‐fold higher than the control. These results demonstrate that BnMTL (i) is highly expressed in the root following exposure to Cd2+ and (ii) encodes a typical metallothionein‐like protein with high cadmium‐binding activity. [ABSTRACT FROM AUTHOR]

Abstract: Ramie, Boehmeria nivea (L.) Gaudich, family Urticaceae, is a plant native to eastern Asia, and one of the world's oldest fibre crops. It is also used as animal feed and for the phytoremediation of heavy metal‐contaminated farmlands. Thus, the genome sequence of ramie was determined to explore the molecular basis of its fibre quality, protein content and phytoremediation. For further understanding ramie genome, different paired‐end and mate‐pair libraries were combined to generate 134.31 Gb of raw DNA sequences using the Illumina whole‐genome shotgun sequencing approach. The highly heterozygous B. nivea genome was assembled using the Platanus Genome Assembler, which is an effective tool for the assembly of highly heterozygous genome sequences. The final length of the draft genome of this species was approximately 341.9 Mb (contig N50 = 22.62 kb, scaffold N50 = 1,126.36 kb). Based on ramie genome annotations, 30,237 protein‐coding genes were predicted, and the repetitive element content was 46.3%. The completeness of the final assembly was evaluated by benchmarking universal single‐copy orthologous genes (BUSCO); 90.5% of the 1,440 expected embryophytic genes were identified as complete, and 4.9% were identified as fragmented. Phylogenetic analysis based on single‐copy gene families and one‐to‐one orthologous genes placed ramie with mulberry and cannabis, within the clade of urticalean rosids. Genome information of ramie will be a valuable resource for the conservation of endangered Boehmeria species and for future studies on the biogeography and characteristic evolution of members of Urticaceae. [ABSTRACT FROM AUTHOR]