Characteristics of Brassica napus L. metallothionein genes: expression in organs and during seed germination

Abstract

The aim of this work was to identify rape metallotionein genes belonging to all four types of plant MTs and study their expression pattern in rape’s organs and during seed imbibition. Using EST sequences found in NCBI database we have identified four metallothionein genes, BnMT1-4, from Brassica napus L. Analysis of their predicted amino acid sequences confirmed the presence of numerous cysteine residues confirming that these genes encode plant metallothioneins. Both cloned MT nucleotide e and amino acid sequences share the most homology with MT gene sequences from the Brassicaceae family. The BnMT1, BnMT2 and BnMT4 genes harbour one intron, whereas the BnMT3 gene contains two. Examining MT expression by sqRT-PCR in rape cotyledons, leaves, flowers, roots, and hypocotyls demonstrated that BnMT1 is expressed in each organ except the flower. BnMT2 and BnMT3 transcripts are present in all studied organs. Five-day-old cotyledons exhibited the strongest MT expression, whereas mature organs exhibited lower or approximately similar levels of expression. BnMT4 expression was not observed in the organs; however, it was observed in dry and germinating rape seeds. Additionally, BnMT1 and BnMT2 are expressed both in dry and germinating seeds. BnMT3 transcripts were not observed in dry seeds but were apparent at the 24th hour of imbibition, During the next 12 hours the expression level of BnMT3 increases approximately 6-fold and lasts through the 5th day, when the seedling develops. The results suggest that BnMT4 may regulate germination processes. Organ-specific expression of rape MTs was demonstrated, suggesting that these genes play significant roles in embryogenesis, pollen germination, fruit ripening, senescence and thus may potentiate proper plant development