Glutathione binding to the plant At Atm3 transporter and implications for the conformational coupling of ABC transporters

The ATP Binding Cassette (ABC) transporter of mitochondria (Atm) from Arabidopsis thaliana (AtAtm3) has been implicated in the maturation of cytosolic iron-sulfur proteins and heavy metal detoxification, plausibly by exporting glutathione derivatives. Using single-particle cryo-electron microscopy, we have determined structures of AtAtm3 in multiple conformational states. These structures not only provide a structural framework for defining the alternating access transport cycle, but also highlight an unappreciated feature of the glutathione binding site, namely the paucity of cysteine residues that could potentially form inhibitory mixed disulfides with glutathione. Despite extensive efforts, we were unable to prepare the ternary complex of AtAtm3 with bound GSSG and MgATP. A survey of structurally characterized type IV ABC transporters that includes AtAtm3 establishes that while nucleotides are found associated with all conformational states, they are effectively required to stabilize occluded and outward-facing conformations. In contrast, transport substrates have only been observed associated with inward-facing conformations. The absence of structures containing both nucleotide and transport substrate suggests that this ternary complex exists only transiently during the transport cycle.

Effects of Intercropping Patterns on Cadmium Tolerance of Perilla Frutescens and Soybean

In this study, we intercropped hyperaccumulator Perilla frutescens with soybean to explore the effects of intercropping under cadmium stress based on the physiological growth indexes of plant, cadmium absorption capacity, and soil cadmium forms Experiments showed that compared with mono-cropping, intercropping soybean’s biomass, catalase (CAT) activity, peroxidase (POD) activity, total chlorophyll and net photosynthetic rate were significantly increased by 1042%~10658%, 1578%~7381%, 1345%~2337%, 376%~1500% and 7121%~31278%, while P frutescens’s significantly decreased by 9387%~9507%, 1562%~2572%, 12056%~15331%, 715%~756% and 3056%~5076% Under 5 and 10 mg kg-1 Cd treatments, the Cd content in roots, stems, leaves, pods and grains of intercropping soybean decreased significantly by 1072%~3174%, 1488%~2168%, 1995%~3413%, 2222%~5270% and 791%~1786% along with enrichment coefficient decreasing by 1486%~2787%, while those of P frutescens significantly increased by 8700%~2141%, 948%~2155%, 2305%~3766% and 1818%~9412% along with enrichment coefficient significantly increasing by 2000%~7775% Additionally, citric acid, succinic acid, oxalic acid and tartaric acid worked importantly in heavy metal detoxification in plants Strikingly, the content of soil exchangeable Cd (EXC) under intercropping was the highest, even higher than that of mono-cropping soybean and P frutescens, which accounted for 37%~42% under the same stress condition Therefore, intercropping Perilla frutescens with soybean provide a potential strategy for Cd phytoremediation

Comparative and Systematic Omics Revealed Low Cd Accumulation of Potato StMTP9 in Yeast: Suggesting a New Mechanism for Heavy Metal Detoxification

The metal tolerance protein (MTP) family is a very old family with evolutionary conservation and less specific amplification. It seems to retain the original functions of the ancestral genes and plays an important role in maintaining metal homeostasis in plant cells. We identified the potato MTP family members for the first time, the specific and conservative StMPTs were discovered by using systematic and comparative omics. To be surprised, members of the StMTP family seem to have mutated before the evolution of dicotyledon and monocotyledon, and even the loss of the entire subfamily (subfamily G6, G7). Interestingly, StMTP9 represents the conserved structure of the entire subfamily involved in toxic metal regulation. However, the gene structure and transmembrane domain of StMTP8 have undergone specific evolution, showing that the transmembrane domain (Motif13) located at the NH2 terminal has been replaced by the signal peptide domain, so it was selected as the control gene of StMTP9. Through real-time fluorescence quantitative analysis of StMTPs under Cd and Zn stress, a co-expression network was constructed, and it was found that StMTP9 responded significantly to Cd stress, while StMTP8 did the opposite. What excites us is that by introducing StMTPs 8/9 into the ∆ycf1 yeast cadmium-sensitive mutant strain, the functional complementation experiment proved that StMTPs 8/9 can restore Cd tolerance. In particular, StMTP9 can greatly reduce the cadmium content in yeast cells, while StMTP8 cannot. These findings provide a reference for further research on the molecular mechanism of potato toxic metal accumulation.

Heavy Metal -Induced Oxidative Stress And Alteration In Secretory Proteins In Yeast Isolates

In the recent years, yeasts have evolved as potent bioremediative candidates for the detoxification of xenobiotic compounds found in the natural environment. Candida sp. are well studied apart from Saccharomyces in heavy metal detoxification mechanisms. In the current study, Candida parapsilosis strain ODBG2, Candida sp. strain BANG3 and Candida viswanathii strain ODBG4 were isolated from industrial effluents and contaminated ground water were studied for their metal tolerance. Among these three isolates, the metal tolerance was found to be more towards Lead (Pb 2mM), followed by Cadmium (Cd 1.5mM) and Chromium (Cr(VI), 1mM). On further exploring the involvement of primary defensive enzymes in these isolates exhibited towards metal tolerance, the anti-oxidative enzyme Superoxide dismutase (SOD) was found to be prominently high as 25% during first 24h of metal-isolate interaction. In the Catalase (CAT) enzyme assay, it was observed that, the increased enzyme activity at 48h also triggered the activity of peroxidases (PO), which lead to the increase in reduced glutathione (GSH) in the organism by 0.87-1.9 folds, as a metal chelator and also as a second line of defensive molecule. The exoproteome profile showed the early involvement (exponential growth phase) of secreted proteins (low molecular weight) of about ~40-45kDa under Cd and Pb stress (0.5mM). The exoproteome profiling under heavy metal stress in Candida parapsilosis strain ODBG2 and Candida viswanathii strain ODBG4 is the first report.

Phytochelatin Synthase in Heavy Metal Detoxification and Xenobiotic Metabolism

Phytochelatin synthase (PCS) is well-known for its role in heavy metal detoxification in plants, yeasts and non-vertebrate animals. It is a protease-like enzyme that catalyzes glutathione (GSH) to form phytochelatins (PCs), a group of Cys-rich and non-translational polypeptides with a high affinity to heavy metals. In addition, PCS also functions in xenobiotic metabolism by processing GS-conjugates in the cytosol. Because PCS is involved in GSH metabolism and the degradation of GS-conjugates, it is one of the important components in GSH homeostasis and GSH-mediated biodegradation. This chapter reviews the biochemical mechanism of PCS, how the enzyme activity is regulated, and its roles in heavy metal detoxification as well as GS-S-conjugate metabolism. This chapter also highlights the potential applications of PCS in the improvement of plant performance under combined stresses.

Transcriptome Response to Cadmium Exposure in Barley (Hordeum vulgare L.)

Cadmium is an environmental pollutant with high toxicity that negatively affects plant growth and development. To understand the molecular mechanisms of plant response to cadmium stress, we have performed a genome-wide transcriptome analysis on barley plants treated with an increased concentration of cadmium. Differential gene expression analysis revealed 10,282 deregulated transcripts present in the roots and 7,104 in the shoots. Among them, we identified genes related to reactive oxygen species metabolism, cell wall formation and maintenance, ion membrane transport and stress response. One of the most upregulated genes was PLANT CADMIUM RESISTACE 2 (HvPCR2) known to be responsible for heavy metal detoxification in plants. Surprisingly, in the transcriptomic data we identified four different copies of the HvPCR2 gene with a specific pattern of upregulation in individual tissues. Heterologous expression of all five barley copies in a Cd-sensitive yeast mutant restored cadmium resistance. In addition, four HvPCR2 were located in tandem arrangement in a single genomic region of the barley 5H chromosome. To our knowledge, this is the first example showing multiplication of the PCR2 gene in plants.