Heterologous expression of the Leymus chinensis metallothionein gene LcMT3 confers enhanced tolerance to salt stress in Escherichia coli, yeast, and Arabidopsis thaliana

Salinity is poisonous to various plant physiological processes and poses an increasingly severe threat to agricultural productivity worldwide. As a tactic to mitigate this issue, the hunt for salt-tolerance genes and pathways is intensifying. The low-molecular-weight proteins known as metallothioneins (MTs) can effectively reduce salt toxicity in plants. In seeking concrete evidence of its function under salt stress conditions, a unique salt-responsive metallothionein gene, LcMT3, was isolated from the extremely salt-enduring Leymus chinensis and heterologously characterized in Escherichia coli (E. coli), yeast (Saccharomyces cerevisiae), as well as Arabidopsis thaliana. Overexpression of LcMT3 imparted resistance to salt in E. coli cells and yeast, while the development of control cells was completely inhibited. Besides, transgenic plants expressing LcMT3 exhibited significantly enhanced salinity tolerance. They had higher germination rates and longer roots than their nontransgenic counterparts during NaCl tolerance. For several physiological indices of salt tolerance, transgenic lines reduced the accumulation of malondialdehyde (MDA), relative conductivity, and reactive oxygen species (ROS) in comparison to nontransgenic Arabidopsis. They also possessed increased concentrations of proline (Pro), relative water content, chlorophyll content, coupled with three more active antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)). Transgenic plants also accumulated less Na+ and maintained a lower Na+/K+ ratio than control, which can be attributable to the transgene's regulatory effect on transporter proteins such as salt overly sensitive (SOS) and Na+/H+ antiporter (NHX1), as demonstrated by qPCR experiments. Collectively, LcMT3 could have a vital function in salinity resistance and be an essential candidate protein for abiotic stress.

Different responses in metallothionein gene expression and antioxidative enzyme activity lead to more ROS accumulation in rice exposed to Tl(III) than to Tl(I)

This is the first study to investigate the reduction mechanism of Tl (III) to Tl(I) in the presence of plants, especially rice. Smaller plant density could effectively reduce the content of organic acids in the hydroponic system to keep the stability of Tl(III). As the plant density was reduced from 40 seedlings to 10 seedlings in 100 mL Tl(III) solution, the content of oxalate was declined to one-third of the original, and the ratio of Tl(III)/total Tl was increased from 39.6% to 81.0% in the first 2 h treatment. Then the differences in antioxidant capacity of rice exposed to the two Tl species were studied. The contents of malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and superoxide anion (O₂˙^-) of rice roots exposed to Tl(III) were all higher than those to Tl(I). Meanwhile, the catalase (CAT) activity was significantly depressed and peroxidase (POD) was increased by Tl(III), whereas superoxide dismutase (SOD) showed a rise in both Tl(I) and Tl(III) with no significant difference between them. The expression of metallothionein gene OsMT1a to Tl(I) was upregulated to 255.5 times of Tl(III) though OsMT2c was downregulated to 0.39 times of Tl(III). Overall, the different responses in metallothionein gene expression and antioxidative enzyme activation might result in more ROS accumulation to rice roots by Tl(III) treatment than those by Tl(I).

Cadmium in vivo exposure alters stress response and endocrine-related genes in the freshwater snail Physa acuta. New biomarker genes in a new model organism

The freshwater snail Physa acuta is a sensitive organism to xenobiotics that is appropriate for toxicity testing. Cadmium (Cd) is a heavy metal with known toxic effects on several organisms, which include endocrine disruption and activation of the cellular stress responses. There is scarce genomic information on P. acuta; hence, in this work, we identify several genes related to the hormonal system, the stress response and the detoxification system to evaluate the effects of Cd. The transcriptional activity of the endocrine-related genes oestrogen receptor (ER), oestrogen-related receptor (ERR), and retinoid X receptor (RXR), the heat shock proteins genes hsp70 and hsp90 and a metallothionein (MT) gene was analysed in P. acuta exposed to Cd. In addition, the hsp70 and hsp90 genes were also evaluated after heat shock treatment. Real-time reverse transcriptase-polymerase chain reaction (qRT-PCR) analysis showed that Cd presence induced a significant increase in the mRNA levels of ER, ERR and RXR, suggesting a putative mode of action that could explain the endocrine disruptor activity of this heavy metal at the molecular level on Gastropoda. Moreover, the hsp70 gene was upregulated after 24-h Cd treatment, but the hsp90 gene expression was not affected. In contrast, the hsp70 and hsp90 genes were strongly upregulated during heat shock response. Finally, the MT gene expression showed a non-significant variability after Cd exposure. In conclusion, this study provides, for the first time, information about the effects of Cd on the endocrine system of Gastropoda at the molecular level and offers new putative biomarker genes that could be useful in ecotoxicological studies, risk assessment and bioremediation.