Optimization of hydrolysis conditions of crop straw and its effect in Chlorella sorokiniana culture.

Taking straws of corn, wheat, and millet as raw materials, we pretreated them with alkaline hydrogen peroxide, and then hydrolyzed by cellulase and xylanase. We selected the total sugar content in the hydrolysate as the indicator to evaluate the hydrolysis of the straws from three crop species, and further optimized the conditions. Then, the hydrolysates of three types of crop straws were used as carbon source for Chlorella sorokiniana culture to assess their effects on microalgal cultivation. The results showed that the optimal hydrolysis conditions for the three crop straws were identified as solid-liquid ratio of 1:15, temperature of 30 ℃, and treatment time of 12 h. Under such optimal condition, the total sugar contents increased up to 1.677, 1.412, and 1.211 g·L-1 in the corn, millet and wheat straw hydrolysate, respectively. The hydrolysates from the three crop straw could significantly increase both algal biomass and lipid content of C. sorokiniana. Corn straw hydrolysate had the best effect, with high levels of algal biomass (1.801 g·L-1) and lipid content (30.1%). Therefore, we concluded that crop straw hydrolysates as carbon source could significantly promote microalgal biomass and lipid enrichment. The results could lay the foundation for the efficient conversion and utilization of straw lignocellulose raw materials, provide new knowledge for the resource utilization of agricultural wastes, as well as the theoretical basis for the efficient cultivation of microalgae using crop straw hydrolysates.

Identification of differentially expressed genes associated with aluminum resistance in the soybean plant.

Aluminum (Al) toxicity is a major limitation to crop production in countries where acidic soil is abundant. In China, soybean production is constrained by Al stress-induced toxicity. As such, there is growing interest to develop Al-resistant varieties. In the present study, we sought to determine potential genes, functions and pathways for screening and breeding of Al-resistant varieties of soybean. First, we mined the E-GEOD-18517 dataset and identified 729 differentially expressed genes (DEGs) between untreated and Al-treated groups. Next, we performed Gene Ontology and Kyoto Encyclopedia of Genes and Genome pathways enrichment analysis and observed that most of the screened genes were mainly enriched in defense response, plasma membrane and molecular transducer activity. They were also enriched in three important pathways, the phenylpropanoid biosynthesis, plant-pathogen interaction, and cutin, suberine and wax biosynthesis. Utilizing weighted gene co-expression network analysis of 815 DEGs screened by Venn diagram, we identified DEGs that were the most disparate between treated and untreated groups. LOC100793667 (probable protein phosphatase 2C 60, GLYMA_17G223800), LOC100780576 (ethylene-responsive transcription factor 1B, GLYMA_02G006200), and LOC100785578 (protein ESKIMO 1, GLYMA_02G258000) were the most differentially expressed, which were consistent with the qRT-PCR results. As these genes are known to participate in essential functions, such as cell junction and phenylpropanoid biosynthesis, these genes may be important for breeding Al-resistant varieties. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-01018-x.

Integration of Metabolome and Transcriptome Studies Reveals Flavonoids, Abscisic Acid, and Nitric Oxide Comodulating the Freezing Tolerance in Liriope spicata.

Liriope spicata is an evergreen perennial ornamental groundcover with a strong freezing tolerance. However, the molecular mechanism underlying the freezing tolerance in L. spicata remains unclear. In this study, a comprehensive investigation of L. spicata freezing tolerance was conducted at the levels of physiology and biochemistry, metabolite, and transcript during the stress treatment. There were 581 unique differentially expressed metabolites (DEMs) and 10,444 unique differentially expressed genes (DEGs) between freezing treatment and normal cultured plant in leaves. Integrated analysis of metabolomics and transcriptomics showed that flavonoid biosynthesis, carbohydrate metabolism, amino acid metabolism, lipid metabolism, and signal transduction pathways were prominently enriched in response to the freezing stress in L. spicata. Now, we identified genes and metabolites involved in the flavonoid pathway, abscisic acid (ABA) biosynthesis, and the oxidative synthesis pathway of nitric oxide (NO), which may form a regulatory network and play a synergistic effect in osmotic adjustment, reactive oxygen species (ROS) homeostasis, and stomatal closure under freezing stress. These results offer a comprehensive network of flavonoids, ABA, and NO comodulating the freezing tolerance in L. spicata.

High-throughput sequencing reveals the molecular mechanisms determining the stay-green characteristic in soybeans.

Senescence is an internally systematized degeneration process leading to death in plants. Leaf yellowing, one of the most prominent features of plant aging may lead to reduced crop yields. The molecular mechanism of responses to senescence in soybean leaves is not completely clear. In our research, two soybean varieties were selected with different stay-green traits: stay-green variety (BN106) and non-stay-green variety (KF14). RNA samples extracted from the leaves of two varieties were sequenced and compared using high-throughput sequencing. Six key enzyme genes in chlorophyll degradation pathways were studied to analyze the changes in their expression at seedling, flowering and maturation stage. Meanwhile, the construction of the genetic transformation process had been constructed to identify the function of putative gene by RNA-interference. A total of 4329 DEGs were involved in 52 functional groups and 254 KEGG pathways. Twelve genes encoding senescence-associated and inducible chloroplast stay-green protein showed significant differential expression. MDCase and PAO have a significant expression in BN106 that may be the key factors affecting the maintenance of green characteristics. In addition, the function of GmSGRs has been identified by genetic transformation. The loss of GmSGRs may cause soybean seeds to change from yellow to green. In summary, our results revealed fundamental information about the molecular mechanism of aging in soybeans with different stay-green characteristics. The work of genetic transformation lays a foundation for putative gene function studies that could contribute to postpone aging in soybeans.

[Symbiotic bacteria facilitate algal growth and oil biosynthesis in Scenedesmus obliquus]. / å ±ç”ŸèŒä¿ƒè¿›æ–œç”Ÿæ 藻生长和油脂合成.

We isolated bacteria from the phycosphere of Scenedesmus obliques and sequenced 16S rDNAs to establish algae-bacterial co-culture systems. Further, we examined effects of the bacteria on algal growth, and parameters associated with physio-biochemical and oil-producing characteristics of S. obliquus. Seven bacterial strains were isolated, including Micrococcus (strains 1-1, 1-2 and 1-3), Pseudomonas sp. (strains 2-1 and 2-2), Exiguobacterium (strain-3) and Staphylococcus sp. (strain-4). Among them, two bacteria (strain 1-2 and strain 2-1) were characterized as the dominant growth-promoting bacterial strains, which significantly increased algal growth, pigment production, and oil enrichment. After eight days cultivation under microalgal-bacterial (strain 1-2) symbiotic systemat at an initial ratio of 1:10, biomass of S. obliquus was 4.27 g·L-1, about 46.0% higher than that of the control. The contents of chlorophyll a, chlorophyll b and carotenoids were increased by 12.1%, 16.7% and 25.0%, respectively. Oil content was increased by 14.0% and reached to 25.7%, and the oleic acid content was significantly higher than that of the control and up to 16.4%. When co-cultured with Pseudomonas sp. (strain 2-1) for eight days at an initial ratio of 1:5, algal biomass, chlorophyll a, chlorophyll b and carotenoids contents were higher than that of the control by 47.9%, 16.0%, 17.5% and 19.9%, respectively. The total oil (27.1%) and oleic acid (18.2%) contents were increased by 20.4% and 64.0%, respectively. We concluded that Micrococcus (strain 1-2) and Pseudomonas sp. (strain 2-1) could significantly promote algal growth and increase oil production by their beneficial interaction with S. obliques, which could be potentially used in commercial production of S. obliques.

Splice Variants of the Castor WRI1 Gene Upregulate Fatty Acid and Oil Biosynthesis When Expressed in Tobacco Leaves.

The plant-specific WRINKLED1 (WRI1) is a member of the AP2/EREBP class of transcription factors that positively regulate oil biosynthesis in plant tissues. Limited information is available for the role of WRI1 in oil biosynthesis in castor bean (Ricinus connunis L.), an important industrial oil crop. Here, we report the identification of two alternatively spliced transcripts of RcWRI1, designated as RcWRI1-A and RcWRI1-B. The open reading frames of RcWRI1-A (1341 bp) and RcWRI1-B (1332 bp) differ by a stretch of 9 bp, such that the predicted RcWRI1-B lacks the three amino acid residues "VYL" that are present in RcWRI1-A. The RcWRI1-A transcript is present in flowers, leaves, pericarps and developing seeds, while the RcWRI1-B mRNA is only detectable in developing seeds. When the two isoforms were individually introduced into an Arabidopsiswri1-1 loss-of-function mutant, total fatty acid content was almost restored to the wild-type level, and the percentage of the wrinkled seeds was largely reduced in the transgenic lines relative to the wri1-1 mutant line. Transient expression of each RcWRI1 splice isoform in N. benthamiana leaves upregulated the expression of the WRI1 target genes, and consequently increased the oil content by 4.3-4.9 fold when compared with the controls, and RcWRI1-B appeared to be more active than RcWRI1-A. Both RcWRI1-A and RcWRI1-B can be used as a key transcriptional regulator to enhance fatty acid and oil biosynthesis in leafy biomass.

Expression of yeast acyl-CoA-∆9 desaturase leads to accumulation of unusual monounsaturated fatty acids in soybean seeds.

An acyl-CoA-Δ9 desaturase from Saccharomyces cerevisiae was expressed by subcellular-targeting in soybean (Glycine max) seeds with the goal of increasing palmitoleic acid (16:1Δ9), a high-valued fatty acid (FA), and simultaneously decreasing saturated FA in oil. The expression resulted in the conversion of palmitic acid (16:0) to 16:1Δ9 in soybean seeds. 16:1Δ9 and its elongation product cis-vaccenic acid (18:1Δ11) were increased to 17 % of the total fatty acids by plastid-targeted expression of the enzyme. Other lipid changes include the decrease of polyunsaturated FA and saturated FA, suggesting that a mechanism exists downstream in oil biosynthesis to compensate the FA alternation. This is the first time a cytosolic acyl-CoA-∆9 desaturase is functionally expressed in plastid and stronger activity was achieved than its cytosolic expression. The present study provides a new strategy for converting 16:0 to 16:1Δ9 by engineering acyl-CoA-Δ9 desaturase in commercialized oilseeds.

[Sequence polymorphism and mapping of wheat Ca2+-binding protein TaCRT-A gene].

Taking thirty-seven hexaploid wheat (AABBDD) accessions with different drought resistance at seedling stage, three wheat species with A genome (AA), and three tetraploid wheat species (AABB) as test materials, and by direct sequencing the single nucleotide polymorphism (SNP) in TaCRT-A, this paper analyzed the relationships of the SNP with the drought resistance of wheat ( Triticum aestivum) at its seedling stage, and mapped the TaCRT-A on the chromosome of wheat. The full-length sequence of the TaCRT-A genomic DNA was 3887 bp. A total of 202 nucleotide variant loci were observed in the full length sequence of 167141 bp, among which, 165 SNP and 37 InDel with the frequencies of 1 SNP/1013 bp and 1 InDel/4517 bp were detected, respectively. The nucleotide diversity (pi) in coding region of TaCRT-A was lower than that in non-coding region, suggesting that the selection pressure in coding region was stronger than that in non-coding region. The 43 accessions could be classified as 14 haplotypes (H1-H14) by haploid analysis, among which, H1, H2, and H13 all contained one accession which was the donor species of A genome in common wheat, H16 and H7 had one high drought-resistant accession, H8 comprised tetraploid wheat, drought-resistant accessions, and drought-sensitive accessions, whereas H11 included the wheat accessions with drought-resistance and medium-drought resistance. Though the expression of TaCRT was induced by water stress, no significant relationship was identified between TaCRT-A polymorphism and drought resistance. Using a population of recombinant inbred lines derived from a cross of Opata 85 x W7984, the TaCRT-A was mapped between SSR markers Xmwg30 and Xmwg570 on chromosome 3A, and the genetic distances were 10.5 cM and 49.6 cM from the flanking markers, respectively.

Synthesis and degradation of the major allergens in developing and germinating soybean seed.

Gly m Bd 28K, Gly m Bd 30K and Gly m Bd 60K are the major soybean (Glycine max (L.) Merr.) allergens limiting the consumption of a good protein source for sensitive individuals. However, little is known about their temporal-spatial expression during seed development and upon germination. The present data shows that soy allergens accumulated in both the embryonic axes and cotyledon, but expression patterns differed depending on the specific allergen. Allergens accumulated sooner and to a greater level in cotyledons than in embryonic axes. Gly m Bd 28 began at 14 d after flowering, 7 to 14 d earlier than Gly m Bd 30K and Gly m Bd 60K. Comparatively, their degradation was faster and more profound in embryonic axes than in cotyledons. Gly m Bd 60K began to decline at 36 h after imbibition and remained detectable up to 108 h in cotyledons. In contrast, the Glym Bd 60K protein was reduced at 24 h, and eventually disappeared at 96 h . In cotyledons Gly m Bd 28K first declined at 24 h, then increased from 36 h to 48 h, followed by its large reduction at 72 h after seed germination. These findings provide useful information on soy allergen biosynthesis and will help move forward towards developing a hypoallergenic soybean for safer food.

Calreticulin: conserved protein and diverse functions in plants.

Calreticulin (CRT) is a key Ca2+-binding protein mainly resident in the endoplasmic reticulum (ER), which is highly conserved and extensively expressed in all eukaryotic organisms investigated. The protein plays important roles in a variety of cellular processes including Ca2+ signaling and protein folding. Although calreticulin has been well characterized in mammalian systems, increased investigations have demonstrated that plant CRTs have a number of specific properties different from their animal counterparts. Recent developments on plant CRTs have highlighted the significance of CRTs in plants growth and development as well as biotic and abiotic stress responses. There are at least two distinct groups of calreticulin isoforms in higher plants. Glycosylation of CRT was uniquely observed in plants. In this article, we will describe our current understanding of plant calreticulin gene family, protein structure, cellular localization, and diverse functions in plants. We also discuss the prospects of using this information for genetic improvements of crop plants.

Molecular cloning and characterization of wheat calreticulin (CRT) gene involved in drought-stressed responses.

Calreticulin (CRT) is a highly conserved and ubiquitously expressed Ca(2+)-binding protein in multicellular eukaryotes. CRT plays a crucial role in many cellular processes including Ca(2+) storage and release, protein synthesis, and molecular chaperone activity. To elucidate the function of CRTs in plant responses against drought, a main abiotic stress limiting cereal crop production worldwide, a full-length cDNA encoding calreticulin protein namely TaCRT was isolated from wheat (Triticum aestivum L.). The deduced amino acid sequence of TaCRT shares high homology with other plant CRTs. Phylogenetic analysis indicates that TaCRT cDNA clone encodes a wheat CRT3 isoform. Southern analysis suggests that the wheat genome contains three copies of TaCRT. Subcellular locations of TaCRT were the cytoplasm and nucleus, evidenced by transient expression of GFP fused with TaCRT in onion epidermal cells. Enhanced accumulation of TaCRT transcript was observed in wheat seedlings in response to PEG-induced drought stress. To investigate further whether TaCRT is involved in the drought-stress response, transgenic plants were constructed. Compared to the wild-type and GFP-expressing plants, TaCRT-overexpressing tobacco (Nicotiana benthamiana) plants grew better and exhibited less wilt under the drought stress. Moreover, TaCRT-overexpressing plants exhibited enhanced drought resistance to water deficit, as shown by their capacity to maintain higher WUE (water use efficiency), WRA (water retention ability), RWC (relative water content), and lower MDR (membrane damaging ratio) (P < or = 0.01) under water-stress conditions. In conclusion, a cDNA clone encoding wheat CRT was successfully isolated and the results suggest that TaCRT is involved in the plant response to drought stress, indicating a potential in the transgenic improvements of plant water-stress.

[New strategy for increasing the specific and efficient expression of transgene in plastids].

Plastid gene engineering has become a new way for plant genetic improvements, particularly showing a unique application value in the use of plants as reactors to produce biopharmaceuticals and other important organic compounds. However, plastids only have a semi-autonomous transcription and translation machinery. The transcription of endogenous plastid genes is largely dependent on nuclear-encoded transcription factors. Regulation of foreign gene expression in plastids is influenced by various factors. Several technique strategies for regulation of transgene expression in plastids were reported recently, such as hybrid transcription factor-mediated system, phage T7-based transcription system and bacterial lac suppressor-based system. The application and improvement of these systems will greatly enhance the specific and effective expression of the transgenes, and achieve high-level accumulations of foreign proteins in plastids.

[Metabolic engineering of edible plant oils].

Plant seed oil is the major source of many fatty acids for human nutrition, and also one of industrial feedstocks. Recent advances in understanding of the basic biochemistry of seed oil biosynthesis, coupled with cloning of the genes encoding the enzymes involved in fatty acid modification and oil accumulation, have set the stage for the metabolic engineering of oilseed crops that produce "designer" plant seed oils with the improved nutritional values for human being. In this review we provide an overview of seed oil biosynthesis/regulation and highlight the key enzymatic steps that are targets for gene manipulation. The strategies of metabolic engineering of fatty acids in oilseeds, including overexpression or suppression of genes encoding single or multi-step biosynthetic pathways and assembling the complete pathway for the synthesis of long-chain polyunsaturated fatty acids (e.g. arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid) are described in detail. The current "bottlenecks" in using common oilseeds as "bioreactors" for commercial production of high-value fatty acids are analyzed. It is also discussed that the future research focuses of oilseed metabolic engineering and the prospects in creating renewable sources and promoting the sustainable development of human society and economy.

[Research progress in genetic engineering of plant secondary metabolism].

Secondary metabolism plays an important role in plant life as well as the interaction between plants and environmental factors. Many secondary metabolites derived from plants have been used for the production of medicines, dyes, insecticides, food flavors, fragrances and so on. With increasingly comprehensive understanding of the plant metabolic networks, great progress has been made in the genetic improvement of plant secondary metabolic pathways through gene engineering. Strategies for the genetic engineering of plant secondary metabolism include: (1) enabling the host plant to accumulate a novel desirable compound by transformation of single/multiple enzyme gene (s) or a whole metabolic pathway; (2) decreasing target gene expression or inhibiting competitive metabolic pathway to achieve metabolic flux towards higher production of particular molecules through antisense RNA and RNA interference technologies; (3) effectively manipulating the transcription factors responsible for the metabolic regulation at multiple steps in a given pathway so as to have a great synthesis of the target bio-chemicals. Basing on author's research work on flavonoid synthesis mechanism in soybean seed and its gene engineering, recent progress in the engineering of plant secondary metabolism involved in the synthesis of anthocyanins, flavonoids, alkaloids, terpenoids, benzoic acid derivatives etc are reviewed.

[Improving the nutritional value of plant foods through transgenic approaches].

The most nutrients required in the human diet come from plants. The nutritional quality of plant products affects the human healthy. The advance of molecular cloning and transgenic technology has provided a new way to enhance the nutritional value of plant material. Transgenic modification of plant nutritional value has progressed greatly in the following aspects: improving the quality, composition and levels of protein, starch and fatty acid in different crops; increasing the levels of antioxidants (e.g. carotenoids and flavonoids); breeding the new type of plants with medical value for human. To date, many transgenic plants with nutritional enhancement have been developed. These transgenic plant products could be directly used as human diet or as valued materials in developing the "functional food" with especial nutritional quality and healthy effects after they are approved by a series of evaluations on their safety and nutritional efficiency for human being. We designed new zinc finger transcription factors (ZFP-TFs) that can specifically down-regulate the expression of the endogenous soybean FAD2-1 gene which catalyzes oleic acid to linoleic acid. Seed-specific expression of these ZFP-TFs in transgenic soybean somatic embryos repressed FAD2-1 transcription and increased significantly the levels of oleic acid, indicating that the engineered ZFP-TFs are capable of regulating fatty acid metabolism and modulating the expression of endogenous genes in plants.

[Analysis of additive and AE interaction effects of QTLs controlling plant height, heading date and panicle number in rice (Oryza sativa L.)].

Plant height (PH), heading date (HD) and productive panicle number (PN) are important agronomic trait in rice. Appropriate plant height, heading date and panicle number are prerequisites for the desired high and stable yield level in rice breeding programs. A recombinant inbred line (RIL) population consisting of 304 individuals was derived from a cross between indica varieties Zhong156 and Gumei2, from which a linkage map consisting of 168 RFLP, SSLP, RAPD and RGA markers that distribute on all the 12 rice chromosomes was constructed, and covers 1447.9 cM of the rice genome. The parents and 304 F9 lines were grown in the paddy field in China National Rice Research Institute (CNRRI), Hangzhou, China in 2001. The experiments were carried out in two seasons followed a randomized complete block design. QTLMapper 1.01 was applied to detect QTLs and QTL x environment (QE) interaction for HD (heading data), PH (plant height) and PN (panicle number), and conditional mapping for PH and PN was performed as well. A total of 15 QTLs with significant additive effects were detected, among which 4 QTLs had significant QE interaction. Ten QTLs with additive x additive epistatic effects for PH, HD and PN were detected, among which none showed significant epistatisis x environment interaction. These QTLs explained 12.12%, 1.38% and 5.00% of the total phenotypic variance for PH, HD and PN, respectively, and contributions were generally lower due to the strong epistatic effects. In conditional QTL analysis, the numbers of QTLs showing significant additive and epistatic effects were 7 and 6 for PH, and 3 and 3 for PN, respectively. Among the QTLs having significant additive effects for PH, qPH7-2 showed both additive effects and QE interaction, qPH7-1 and qPH10 showed QE interaction only, and the remaining 4 QTLs showed additive effects only. Each of the 3 QTLs having significant additive effects for PN did not display significant QE interaction. No epistatic QE interactions was detected. In addition, conditional QTL analysis indicated that the expression of QTLs for PH and PN may vary depending on the QTLs for HD.

[Cytochrome p450 genes and their application in plant improvement].

Cytochrome P450s are heme-containing mixed-function oxidases,involving in lots of biochemical reactions. They play an important role in preventing plants from pathogen and insect attacks and environmental stress. Sequence analysis of genomes has revealed that P450 is a gene super-family. Many cytochrome P450s have been characterized and cloned. Some of them have been used in plant genetic improvement. A great progress has been made in using these P450 genes to create the transgenic plants with multiple resistances,male sterility, higher capability to dissolve toxic chemicals and pollutants and effective productivity of high valuable compounds,indicating P450 genes have a broad prospect with great potential application.

[Application of single nucleotide polymorphism in crop genetics and improvement].

Single nucleotide polymorphism(SNP) is the most common type of sequence difference between alleles, which can be used as a kind of high-throughput genetic marker. Several different routes have been developed to discover and identify SNP. These include the direct sequencing of PCR amplicons, electronic SNP(eSNP) and so on. SNP assays have been made in many crop species such as maize and soybean. The elite germplasm of some crops have been narrowed in genetic diversity, increasing the amount of linkage disequilibrium (LD) present and facilitating the association of SNP haplotypes at candidate gene loci with phenotypes. SNP analysis has been broadly used in the field of plant gene mapping, integration of genetic and physical maps, DNA marker-assisted breeding and functional genomics.

Mapping quantitative trait loci for plant height in wheat (Triticum aestivum L.) using a F2:3 population.

To detect quantitative trait loci (QTLs) controlling plant height, the plant height of 240 F2:3 lines derived from the cross of a dwarf wheat line ND3338 with a tall line F390, was assessed in field trials at two locations with three replications in 2000 and 2001. Microsatellite markers were used to construct a framework linkage map containing 215 loci with 21 linkage groups, and covering the whole genome about 3600cM. With the method of interval mapping, seven putative QTLs affecting plant height were detected on chromosomes 1B, 4B (two regions), 6A (two regions), 6D and 7A, respectively. Phenotypic variations explained by each QTL ranged from 5.2% to 50.1%, and in each environment the total putative QTLs explained about 64.8%-75% of the total phenotypic variation respectively. A major QTL located on chromosome arm 4BS near the locus Xgwm113, around the Rht-Blb locus, explained a large part of the phenotypic variation (27.8%-36.2% depending on the years or the locations). Except the QTL on chromosome 7A, all the other QTLs from ND3338 decreased the plant height, variously from 0.94 cm to 9.33 cm. Most of the identified QTLs were consistent in all the environments, and should be useful in future marker-assisted-selection programs for breeding dwarf and semi-dwarf wheat cultivars.

[Genes of metal-binding proteins and their application in bioremediation of heavy metals].

Heavy metal pollution has become a global environmental hazard. The use of microorganisms and plants for the decontamination of heavy metals is recognized as a low lost and high efficiency method for cleaning up metal contamination. It shows that various metal-binding proteins such as metallothioneins (MTs) or phytochelatines (PCs) play an important role in defense systems and detoxification to heavy metals in organisms. Many genes of MTs and PCs have been cloned and utilized successfully in genetically modified bacteria and plants for increasing remediation capacity. These transgenic organisms have been displayed a great potential in bioremediation and phytoremediation of heavy metals.