Characterization and Expression of DNA Sequences Encoding Putative Type-II Metallothioneins in the Seagrass Posidonia oceanica

• Published in: Plant physiology (Bethesda) 2000-08, Vol.123 (4), p.1571-1581
• Main Authors: Giordani, Tommaso, Lucia Natali, Bianca Elena Maserti, Sonia Taddei, Andrea Cavallini
• Format: Article
• Language: English
• Subjects: Accumulation; Amino Acid Sequence; Anthropogenic factors; Aquariums; Biogeochemical cycles; Biological and medical sciences; Blotting, Northern; Blotting, Southern; Cadmium; Copper; Deoxyribonucleic acid; DNA; DNA, Plant - genetics; DNA, Plant - isolation & purification; DNA, Plant - metabolism; Environmental stress; Environmental Stress and Adaptation; Fundamental and applied biological sciences. Psychology; Genes. Genome; Genomics; Indicator species; Introns; Leaves; Magnoliopsida - genetics; Magnoliopsida - metabolism; Marine; Marine organisms; Mercury; Mercury - toxicity; Messenger RNA; Metallothionein - genetics; Metallothionein - isolation & purification; Metallothionein - metabolism; Metallothioneins; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; Nucleotide sequences; Plant Leaves - genetics; Plant Leaves - metabolism; Plants; Polymerase Chain Reaction; Pomt2a gene; Pomt2b gene; Pomt2c gene; Posidonia oceania; Posidonia oceanica; Pseudogenes; RNA; RNA, Messenger - analysis; Sea water; Sequence Alignment; Trace Elements - toxicity; Trace metals
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.123.4.1571

Posidonia oceanica is a marine phanerogram, largely widespread in the Mediterranean sea, representing an important food substrate for many marine organisms. A progressive reduction of P. oceanica meadows has been reported, due to anthropogenic coastal activity. Studying mechanisms by which this species responds to environmental stresses, three DNA sequences putatively encoding metallothioneins (MTs) have been isolated, by PCR. Two sequences, Pomt2a (accession no. AJ249603) and Pomt2b (accession no. AJ249602), show high similarities with genes encoding type-II MTs and are interrupted by two and one intron, respectively. The third sequence, Pomt2c (accession no. AJ249604), is supposed to be a pseudogene, originated by retrotranscription of the Pomt2b mRNA. These sequences belong to a multigene family with at least five members. Northern hybridizations indicated that MT transcripts accumulation is constitutive and seasonally regulated. MT encoding RNAs increase after rhyzome harvesting and (at a lesser extent) after 15 d of cultivation in an aquarium. As for animal MTs, transcripts accumulation is observed also after exposure to trace metals such as copper and cadmium. In the case of copper, the effect depends on concentration. Finally, taking into consideration the great interest in studying the biogeochemical cycle of mercury in the Mediterranean basin and since P. oceanica is commonly considered a bioindicator of this metal, the effect of mercury treatments on the accumulation of MT transcripts has been analyzed: in only a few experiments a small increase in the level of transcripts was recorded, suggesting that MTs are not key elements in the mercury accumulation by this species.