| Mercury (Hg) is one of the most toxic heavy metals. It has become a major contaminant through mining and smelting, untreated industrial wastes, mercury by-products and other livelihood activities, and with significant impacts on growth and development of organisms even human health. Hg is easily taken up by plants and is biochemically toxic because it binds to sulfhydryl groups (-SH) of proteins, resulting in displacement of essential elements or disruption of structure. Further, Mg2+, Mn2+, or Zn2+can be replaced by Hg2+, so the activities of the enzymes with these metals may be disturbed. Anymore, Hg can trigger the generation of reactive oxygen species (ROS) and induce oxidation of-SH or cross-linking of disulfide bonds (-S-S). So it is important and urgent to find the ways for protection of-SH and-S-S, preventing the aggregation of denatured proteins and maintaining the metabolism in order.Protein disulfide isomerase (PDI, EC5.3.4.1) and disulfide isomerase-like protein (PDIL), one member of the thioredoxin super-family, can catalyze thiol-disulfide interchange, resulting in the formation, reduction, or isomerization of protein disulfide bonds in protein substrates. In addition, PDI or disulfide isomerase-like protein (PDIL) display chaperone activity that promote protein folding or prevent protein aggregation. But the relationship of PDIL and plant response under Hg toxicity has not been reported until now. The expression profile of OsPDILs was first investigated in this study, and the enhanced tolerance to mercury was observed in transgenic plants by over-expression of PDIL. The results in details are as follows:1) In silico identification and analysis, including basic information, structural domain, classify, chromosomal location, and expression, of the protein disulphide isomerases in rice were performed, and the results showed the amino acid length of the12OsPDILs was about148aa to563aa. They have one or two domain of the Trx (CXXC) and located in9chromosomals. And the expression analysis from UniGene database or the massively parrellel signature sequencing proved the differences in genes, tissues or stages of growth and development.2) The expression of OsPDILs under Hg treatment was determined by real time quantity-PCR with Oryza saliva L., cv. Nipponbare. The results showed that OsPDIL1-1, OsPDIL1-3, OsPD1L5-1, OsPDIL5-2and OsPDIL5-3were up-regulated in roots of rice seedlings under75μM HgCl2treatments, compared to normal condition, while OsPDIL1-2was down-regulated. And OsPDILs2-1, OsPDILs2-3and OsPDILs5-4showed no significant difference whenever the Hg2+treatment or not.3) MTH1745, a PDIL from Methanothermobacter thermoautotrophicum, was reconstructed and transformed into Arabidopsis thaliana by inflorescence. The homozygous lines were chosen and presented the resistance to Hg stress. They also displayed the tolerance to high-tempreture or salt stress.4) Transgenic rice lines were achieved by co-cultivation of rice calli derived from mature seed scutella with A. tumefaciens containing p1301-35S::MTH1745. The results of RT-PCR indicated a high level of MTH1745mRNA in leaves and roots of these transgenic plants. When treated with different concentration of HgCl2, the transgenic rice seedlings displayed Hg tolerance with obvious phenotypes and more effective photosynthesis (net photosynthetic rate Pn, stomatal conductance Gs and transpiration rate Tr) compared to wild-type plants. Furthermore, antioxidant enzyme activities of superoxide dismutase and peroxidase were notably higher and increased content of non-protein thiols and reduced glutathione (GSH) were also observed. All these may indicate that the transgenic plants could enhance the detoxification of Hg by promoting the synthesis of protein, increasing the activities of compounds with-SH or-S-S, protecting the enzymes in the process of photosynthesis and then proventing the oxidative damage of membrane caused by mercury stress. |
PDF Full Text Request