Expression analysis of buckwheat (Fagopyrum esculentum Moench) metallothionein-like gene (MT3) under different stress and physiological conditions

Offspring of metal contaminated saltmarsh (Juncus acutus) exhibit tolerance to the essential metal Zn but not the nonessential metal Pb

Halophytes residing in metal-contaminated saltmarsh habitats may employ strategies to enhance fitness of the next generation. We aimed to test the hypothesis that Juncus acutus individuals inhabiting metal-contaminated locations would experience elevated tolerance of offspring to metals compared to plants residing in locations with no metal contamination history. J. acutus seeds (F₁ generation) were collected from F₀ parent plants residing at eight locations of a contemporary sediment metal gradient (contaminated to uncontaminated) across the coast of NSW, Australia (Hunter river, Lake Macquarie and Georges River). Seeds were exposed in the laboratory to incremental Zn (0.0-1.6 mM) and Pb (0.0-0.50 mM) for nine (9) days, and % germination, germination rate, root elongation and vigour index were assessed for the determination of tolerance. Greater root accumulation (BCF = 1.01) of Zn and subsequent translocation to aerial parts (culm BCF = 0.58 and capsule BCF = 0.85) were exhibited in parents plants, whereas Pb was excluded from roots (BCF = 0.60) and very little translocation to aerial portions of the plant was observed (culm BCF = 0.02 and capsule BCF = 0.05). F₁ offspring exhibited tolerance to Zn with EC₅₀ (% germination) significantly correlated with their parents' culm (R² = 0.93, p = 0.00) and capsule (R² = 0.57; p = 0.03) Zn. No correlations were observed between offspring Pb tolerance and Pb in parents' plant tissues. Enhanced tolerance to the essential metal Zn may be because Zn is very mobile in the parent plant and seeds experience greater Zn load as a significant portion of sediment Zn reaches capsules (85%). Thus, Zn tolerance in J. acutus seeds is likely attributable to acclimation via maternal transfer of Zn; however, further manipulative experiments are required to disentangle potential acclimation, adaptation or epigenetic effects in explaining the tolerance observed.

Gm1-MMP is involved in growth and development of leaf and seed, and enhances tolerance to high temperature and humidity stress in transgenic Arabidopsis

Matrix metalloproteinases (MMPs) are a family of zinc- and calcium-dependent endopeptidases. Gm1-MMP was found to play an important role in soybean tissue remodeling during leaf expansion. In this study, Gm1-MMP was isolated and characterized. Its encoding protein had a relatively low phylogenetic relationship with the MMPs in other plant species. Subcellular localization indicated that Gm1-MMP was a plasma membrane protein. Gm1-MMP showed higher expression levels in mature leaves, old leaves, pods, and mature seeds, as well as was involved in the development of soybean seed. Additionally, it was involved in response to high temperature and humidity (HTH) stress in R7 leaves and seeds in soybean. The analysis of promoter of Gm1-MMP suggested that the fragment from -399 to -299 was essential for its promoter activity in response to HTH stress. The overexpression of Gm1-MMP in Arabidopsis affected the growth and development of leaves, enhanced leaf and developing seed tolerance to HTH stress and improved seed vitality. The levels of hydrogen peroxide (H2O2) and ROS in transgenic Arabidopsis seeds were lower than those in wild type seeds under HTH stress. Gm1-MMP could interact with soybean metallothionein-II (GmMT-II), which was confirmed by analysis of yeast two-hybrid assay and BiFC assays. All the results indicated that Gm1-MMP plays an important role in the growth and development of leaves and seeds as well as in tolerance to HTH stress. It will be helpful for us understanding the functions of Gm1-MMP in plant growth and development, and in response to abiotic stresses.

De novo sequencing and analysis of the transcriptome of Panax ginseng in the leaf-expansion period

Panax ginseng, a traditional Chinese medicine, is used worldwide for its variety of health benefits and its treatment efficacy. However, it is difficult to cultivate due to its vulnerability to environmental stresses. The present study provided the first report, to the best of our knowledge, of transcriptome analysis of ginseng at the leaf‑expansion stage. Using the Illumina sequencing platform, >40,000,000 high‑quality paired‑end reads were obtained and assembled into 100,533 unique sequences. When the sequences were searched against the publicly available National Center for Biotechnology Information protein database using The Basic Local Alignment Search Tool, 61,599 sequences exhibited similarity to known proteins. Functional annotation and classification, including use of the Gene Ontology, Clusters of Orthologous Groups, and Kyoto Encyclopedia of Genes and Genomes databases, revealed that the activated genes in ginseng were predominantly ribonuclease‑like storage genes, environmental stress genes, pathogenesis-related genes and other antioxidant genes. A number of candidate genes in environmental stress‑associated pathways were also identified. These novel data provide useful information on the growth and development stages of ginseng, and serve as an important public information platform for further understanding of the molecular mechanisms and functional genomics of ginseng.

Expression of the rgMT gene, encoding for a rice metallothionein-like protein in Saccharomyces cerevisiae and Arabidopsis thaliana

Metallothioneins (MTs) are cysteine-rich proteins of low molecular weight with many attributed functions, such as providing protection against metal toxicity, being involved in regulation of metal ions uptake that can impact plant physiology and providing protection against oxidative stress. However, the precise function of the metallothionein-like proteins such as the one coded for rgMT gene isolated from rice (Oryza sativa L.) is not completely understood. The whole genome analysis of rice (O. sativa) showed that the rgMT gene is homologue to the Os11g47809 on chromosome 11 of O. sativa sp. japonica genome. This study used the rgMT coding sequence to create transgenic lines to investigate the subcellular localization of the protein, as well as the impact of gene expression in yeast (Saccharomyces cerevisiae) and Arabidopsis thaliana under heavy metal ion, salt and oxidative stresses. The results indicate that the rgMT gene was expressed in the cytoplasm of transgenic cells. Yeast cells transgenic for rgMT showed vigorous growth compared to the nontransgenic controls when exposed to 7 mM CuCl2, 10 mM FeCl2, 1 M NaCl, 24 mM NaHCO3 and 3.2 mM H2O2, but there was no significant difference for other stresses tested. Similarly, Arabidopsis transgenic for rgMT displayed significantly improved seed germination rates over that of the control when the seeds were stressed with 100 μM CuCl2 or 1 mM H2O2. Increased biomass was observed in the presence of 100 μM CuCl2, 220 μM FeCl2, 3 mM Na2CO3, 5 mM NaHCO3 or 1 mM H2O2. These results indicate that the expression of the rice rgMT gene in transgenic yeast and Arabidopsis is implicated in improving their tolerance for certain salt and peroxide stressors.

A novel metallothionein gene from a mangrove plant Kandelia candel

A new metallothionein (MT) gene was cloned from Kandelia candel, a mangrove plant with constitutional tolerance to heavy metals, by rapid amplification of cDNA ends and named KMT, which is composed of two exons and one intron. The full length of KMT cDNA was 728 bp including 121 bp 5' noncoding domain, 240 bp open reading frame and 384 bp 3' termination. The coding region of KMT represented a putative 79 amino acid protein with a molecular weight of 7.75 kDa. At each of the amino- and carboxy-terminal of the putative protein, cysteine residues were arranged in Cys-Cys, Cys-X-Cys and Cys-X-X-Cys, indicating that the putative protein was a novel type 2 MT. Sequence and homology analysis showed the KMT protein sequence shared more than 60 % homology with other plant type 2 MT-like protein genes. At amino acid level, the KMT was shown homology with the MT of Quercus suber (83 %), of Ricinus communis (81 %) and of Arabidopsis thaliana (64 %). Function studies using protease-deficient Escherichia coli strain BL21 Star ™(DE3) confirmed the functional nature of this KMT gene in sequestering both essential (Zn) and non-essential metals (Cd and Hg) and the E. coli BL21 with KMT can live in 1,000 μmol/L Zn, 120 μmol/L Hg, and 2,000 μmol/L Cd. The information could provide more details of the causative molecular and biochemical mechanisms (including heavy metal sequestration) of the KMT in K. candel or a scientific basis for marine heavy-metal environment remediation with K. candel. This study also provides a great significance of protecting mangrove species and mangrove ecosystem.

Barley metallothioneins: MT3 and MT4 are localized in the grain aleurone layer and show differential zinc binding

Metallothioneins (MTs) are low-molecular-weight, cysteine-rich proteins believed to play a role in cytosolic zinc (Zn) and copper (Cu) homeostasis. However, evidence for the functional properties of MTs has been hampered by methodological problems in the isolation and characterization of the proteins. Here, we document that barley (Hordeum vulgare) MT3 and MT4 proteins exist in planta and that they differ in tissue localization as well as in metal coordination chemistry. Combined transcriptional and histological analyses showed temporal and spatial correlations between transcript levels and protein abundance during grain development. MT3 was present in tissues of both maternal and filial origin throughout grain filling. In contrast, MT4 was confined to the embryo and aleurone layer, where it appeared during tissue specialization and remained until maturity. Using state-of-the-art speciation analysis by size-exclusion chromatography inductively coupled plasma mass spectrometry and electrospray ionization time-of-flight mass spectrometry on recombinant MT3 and MT4, their specificity and capacity for metal ion binding were quantified, showing a strong preferential Zn binding relative to Cu and cadmium (Cd) in MT4, which was not the case for MT3. When complementary DNAs from barley MTs were expressed in Cu- or Cd-sensitive yeast mutants, MT3 provided a much stronger complementation than did MT4. We conclude that MT3 may play a housekeeping role in metal homeostasis, while MT4 may function in Zn storage in developing and mature grains. The localization of MT4 and its discrimination against Cd make it an ideal candidate for future biofortification strategies directed toward increasing food and feed Zn concentrations.

Generation of an expressed sequence tag (EST) library from salt-stressed roots of Jatropha curcas for identification of abiotic stress-responsive genes

Improving salinity and drought tolerance of crop plants has been an important aim of modern agricultural development, which depends on understanding the functions of genes expressed during the process of stress adaptation. EST resources are an efficient and cost-effective solution to gene discovery. Jatropha curcas is emerging as the most promising tree oil seed as a source of biodiesel. To identify genes that respond to abiotic stress, in the present study, we report 1240 ESTs generated from root cDNA libraries of J. curcas. ESTs were clustered and assembled into a collection of 865 unigenes, with 107 contigs and 758 singleton sequences. The putative functions of several ESTs could be assigned by similarity to plant gene sequence comparisons. It was found that 23 full-length CDS (34%) and the majority of transcription factors had sequence similarity to genes known to be involved in abiotic and biotic stress tolerance. The expression pattern of nine selected genes revealed that these genes are differentially expressed in various tissues during adaptation to stress. The data could serve as a critical resource to enable plant improvement programmes towards enhancing the adaptability of J. curcas to growth on marginal lands.

Overexpression of Nelumbo nucifera metallothioneins 2a and 3 enhances seed germination vigor in Arabidopsis

Metallothioneins (MTs) are small, cysteine-rich and metal-binding proteins which are involved in metal homeostasis and scavenging of reactive oxygen species. Although plant MTs have been intensively studied, their roles in seeds remain to be clearly established. Here, we report the isolation and characterization of NnMT2a, NnMT2b and NnMT3 from sacred lotus (Nelumbo nucifera Gaertn.) and their roles in seed germination vigor. The transcripts of NnMT2a, NnMT2b and NnMT3 were highly expressed in developing and germinating sacred lotus seeds, and were dramatically up-regulated in response to high salinity, oxidative stresses and heavy metals. Analysis of transformed Arabidopsis protoplasts showed that NnMT2a-YFP and NnMT3-YFP were localized in cytoplasm and nucleoplasm. Transgenic Arabidopsis seeds overexpressing NnMT2a and NnMT3 displayed improved resistance to accelerated aging (AA) treatment, indicating their significant roles in seed germination vigor. These transgenic seeds also exhibited higher superoxide dismutase activity compared to wild-type seeds after AA treatment. In addition, we showed that NnMT2a and NnMT3 conferred improved germination ability to NaCl and methyl viologen on transgenic Arabidopsis seeds. Taken together, these data demonstrate that overexpression of NnMT2a and NnMT3 in Arabidopsis significantly enhances seed germination vigor after AA treatment and under abiotic stresses.

Tissue expression analysis of FeMT3, a drought and oxidative stress related metallothionein gene from buckwheat (Fagopyrum esculentum)

Metallothionein type 3 (MT3) expression has previously been detected in leaves, fruits, and developing somatic embryos in different plant species. However, specific tissular and cellular localization of MT3 transcripts have remained unidentified. In this study, in situ RNA-RNA analysis revealed buckwheat metallothionein type 3 (FeMT3) transcript localization in vascular elements, mesophyll and guard cells of leaves, vascular tissue of roots and throughout the whole embryo. Changes in FeMT3 mRNA levels in response to drought and oxidative stress, as well as ROS scavenging abilities of the FeMT3 protein in yeast were also detected, indicating possible involvement of FeMT3 in stress defense and ROS related cellular processes.

Tamarix hispida metallothionein-like ThMT3, a reactive oxygen species scavenger, increases tolerance against Cd(2+), Zn(2+), Cu(2+), and NaCl in transgenic yeast

A metallothionein-like gene, ThMT3, encoding a type 3 metallothionein, was isolated from a Tamarix hispida leaf cDNA library. Expression analysis revealed that mRNA of ThMT3 was upregulated by high salinity as well as by heavy metal ions, and that ThMT3 was predominantly expressed in the leaf. Transgenic yeast (Saccharomyces cerevisiae) expressing ThMT3 showed increased tolerance to Cd(2+), Zn(2+), Cu(2+), and NaCl stress. Transgenic yeast also accumulated more Cd(2+), Zn(2+), and NaCl, but not Cu(2+). Analysis of the expression of four genes (GLR1, GTT2, GSH1, and YCF1) that aid in transporting heavy metal (Cd(2+)) from the cytoplasm to the vacuole demonstrated that none of these genes were induced under Cd(2+), Zn(2+), Cu(2+), and NaCl stress in ThMT3-transgenic yeast. H(2)O(2) levels in transgenic yeast under such stress conditions were less than half those in control yeast under the same conditions. Three antioxidant genes (SOD1, CAT1, and GPX1) were specifically expressed under Cd(2+), Zn(2+), Cu(2+), and NaCl stress in the transgenic yeast. Cd(2+), Zn(2+), and Cu(2+) increased the expression levels of SOD1, CAT1, and GPX1, respectively, whereas NaCl induced the expression of SOD1 and GPX1.

Expression and characterization analysis of type 2 metallothionein from grey mangrove species (Avicennia marina) in response to metal stress

Metallothioneins (MTs) are a family of low-molecular-weight cysteine-rich proteins and are thought to play possible roles in metal metabolism or detoxification. To evaluate the roles of metallothioneins in metal homeostasis or tolerance in Avicennia marina, a real-time quantitative PCR protocol was developed to directly evaluate the expression of AmMT2 mRNA, when A. marina seedlings were exposed to different concentrations of zinc (Zn), copper (Cu) or lead (Pb) for 3 and 7d. Real-time quantitative PCR results indicated that the regulation of AmMT2 mRNA expression by Zn, Cu and Pb was strongly dependent on concentration and time of exposure. A significant increase in the transcripts of AmMT2 gene was also found in response to Zn, Cu and Pb, at least under some experimental conditions. When AmMT2 was overexpressed in Escherichia coli BL21 as a carboxy-terminal extension of glutathione-S-transferase (GST), the transgenic bacteria showed an increased tolerance to Zn, Cu, Pb and Cd exposure as compared to control strains. Moreover, GST-AmMT2 was purified from E. coli cells grown in the presence of 400 microM Zn, Cu, Pb or Cd. The purified GST-AmMT2 fusion protein could bind higher levels of all four metals than GST alone. Taken together, these data support the hypothesis that AmMT2 may be involved in processes of metal homeostasis or tolerance in A. marina.

Buckwheat (Fagopyrum esculentum Moench) FeMT3 gene in heavy metal stress: protective role of the protein and inducibility of the promoter region under Cu(2+) and Cd(2+) treatments

The protective role in vivo of buckwheat metallothionein type 3 (FeMT3) during metal stress and the responsiveness of its promoter to metal ions were examined. Increased tolerance to heavy metals of FeMT3 producing Escherichia coli and cup1(Delta) yeast cells was detected. The defensive ability of buckwheat MT3 during Cd and Cu stresses was also demonstrated in Nicotiana debneyii leaves transiently expressing FeMT3. In contrast to phytochelatins, the cytoplasmatic localization of FeMT3 was not altered under heavy metal stress. Functional analysis of the corresponding promoter region revealed extremely high inducibility upon Cu(2+) and Cd(2+) treatments. The confirmed defense ability of FeMT3 protein in vivo and the great responsiveness of its promoter during heavy metal exposure make this gene a suitable candidate for biotechnological applications.

Expression analysis of type 2 metallothionein gene in mangrove species (Bruguiera gymnorrhiza) under heavy metal stress

In this paper, we aimed to assess the roles of metallothioneins (MTs) in heavy metal tolerance by analyzing the expression level of BgMT2 in leaves of Bruguiera gymnorrhiza in response to heavy metals. Eight-month-old B. gymnorrhiza seedlings were exposed to different concentrations of zinc (Zn), copper (Cu) or lead (Pb) for 1, 3 and 7 d. A Real-time quantitative PCR protocol was developed to directly evaluate the expression of BgMT2, using 18S rRNA as a reference gene. Real-time quantitative PCR analysis demonstrated BgMT2 mRNA expression was regulated by Zn, Cu and Pb, but the regulation pattern was different for the three metals tested. Significant increase in the transcript level of BgMT2 was also found in response to Zn, Cu and Pb in some experimental conditions. Our results confirm that BgMT2 gene is involved in the regulation of Zn, Cu and Pb in B. gymnorrhiza leaves.

Comparative analyses of genotype dependent expressed sequence tags and stress-responsive transcriptome of chickpea wilt illustrate predicted and unexpected genes and novel regulators of plant immunity

BACKGROUND

The ultimate phenome of any organism is modulated by regulated transcription of many genes. Characterization of genetic makeup is thus crucial for understanding the molecular basis of phenotypic diversity, evolution and response to intra- and extra-cellular stimuli. Chickpea is the world's third most important food legume grown in over 40 countries representing all the continents. Despite its importance in plant evolution, role in human nutrition and stress adaptation, very little ESTs and differential transcriptome data is available, let alone genotype-specific gene signatures. Present study focuses on Fusarium wilt responsive gene expression in chickpea.

RESULTS

We report 6272 gene sequences of immune-response pathway that would provide genotype-dependent spatial information on the presence and relative abundance of each gene. The sequence assembly led to the identification of a CaUnigene set of 2013 transcripts comprising of 973 contigs and 1040 singletons, two-third of which represent new chickpea genes hitherto undiscovered. We identified 209 gene families and 262 genotype-specific SNPs. Further, several novel transcription regulators were identified indicating their possible role in immune response. The transcriptomic analysis revealed 649 non-cannonical genes besides many unexpected candidates with known biochemical functions, which have never been associated with pathostress-responsive transcriptome.

CONCLUSION

Our study establishes a comprehensive catalogue of the immune-responsive root transcriptome with insight into their identity and function. The development, detailed analysis of CaEST datasets and global gene expression by microarray provide new insight into the commonality and diversity of organ-specific immune-responsive transcript signatures and their regulated expression shaping the species specificity at genotype level. This is the first report on differential transcriptome of an unsequenced genome during vascular wilt.

Functional analysis of the buckwheat metallothionein promoter: tissue specificity pattern and up-regulation under complex stress stimuli

To shed light on expression regulation of the metallothionein gene from buckwheat (FeMT3), functional promoter analysis was performed with a complete 5' regulatory region and two deletion variants, employing stably transformed tobacco plants. Histochemical GUS assay of transgenic tobacco lines showed the strongest signals in vascular elements of leaves and in pollen grains, while somewhat weaker staining was observed in the roots of mature plants. This tissue specificity pattern implies a possible function of buckwheat MT3 in those tissues. Quantitative GUS assay showed strong up-regulation of all three promoter constructs (proportional to the length of the regulatory region) in leaves submerged in liquid MS medium containing sucrose, after a prolonged time period. This represented a complex stress situation composed of several synergistically related stress stimuli. These findings suggest complex transcriptional regulation of FeMT3, requiring interactions among a number of different factors.

OsMT1a, a type 1 metallothionein, plays the pivotal role in zinc homeostasis and drought tolerance in rice

Metallothioneins (MTs) are small, cysteine-rich, metal-binding proteins that may be involved in metal homeostasis and detoxification in both plants and animals. OsMT1a, encoding a type 1 metallothionein, was isolated via suppression subtractive hybridization from Brazilian upland rice (Oryza sativa L. cv. Iapar 9). Expression analysis revealed that OsMT1a predominantly expressed in the roots, and was induced by dehydration. Interestingly, the OsMT1a expression was also induced specifically by Zn(2+) treatment. Both transgenic plants and yeasts harboring OsMT1a accumulated more Zn(2+) than wild type controls, suggesting OsMT1a is most likely to be involved in zinc homeostasis. Transgenic rice plants overexpressing OsMT1a demonstrated enhanced tolerance to drought. The examination of antioxidant enzyme activities demonstrated that catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) were significantly elevated in transgenic plants. Furthermore, the transcripts of several Zn(2+)-induced CCCH zinc finger transcription factors accumulated in OsMT1a transgenic plants, suggesting that OsMT1a not only participates directly in ROS scavenging pathway but also regulates expression of the zinc finger transcription factors via the alteration of Zn(2+) homeostasis, which leads to improved plant stress tolerance.

Type 3 metallothioneins respond to water deficit in leaf and in the cambial zone of white poplar (Populus alba)

The involvement of metallothioneins (MTs) in response to plant water stress and recovery was assessed by analyzing gene expression in leaves and in the cambial zone of white poplar. One-year-old plants were submitted to two different watering regimes: irrigation was withheld for 9d and then resumed until day 17, or soil moisture was maintained to field capacity by irrigation during the experiment. Changes in leaves and stem water relations, gas exchange and CO(2) assimilation were recorded. The expression profiles of MT genes were analyzed in developing leaves and the cambial zone at maximum stress levels and after recovery and compared with the watered controls. Whole-plant water relations were significantly affected by water deprivation, though a complete recovery of plant water status was reached after resumption of watering. Withholding irrigation resulted in a significant decrease of leaf turgor potential and relative water content without a significant increase of the osmotic potential at full turgor. Similarly, stem water content decreased, leading to a marked increase of stem shrinkage, confirming that mild water stress affected primarily tissue water status. Following water depletion, the transcript analysis of MT genes revealed increased expression of type 3a and 3b MT genes in cambial tissues, and particularly in leaves. After water resumption, transcription decreased, suggesting that the changes in gene expression were related to water deficit. The results indicate that in leaves and, for the first time, in the cambial zone, type 3 MTs respond in a specific manner to changes in water status. These results are consistent with the regulatory cis-elements present in the 5' flanking region of type 3 MT genes.

Cloning and characterization of TsMT3, a type 3 metallothionein gene from salt cress (Thellungiella salsuginea)

A full-length type 3 plant metallothionein cDNA was isolated from 200 mM NaCl stressed shoots of the salt cress (Thellungiella salsuginea). The 447 bp TsMT3 cDNA sequence has a 207 bp open reading frame (ORF) and encodes a deduced 69 residue peptide of molecular weight 7.52 kDa. Southern blot analysis indicates that, there is only one copy of TsMT3 in the T. salsuginea genome. The accumulation of TsMT3 mRNA is enhanced by the stress imposed by PEG6000, 200 mM NaCl, 50 microM ABA, 4 degrees C, 40 microM CuSO(4) or 25 microM CdCl2. The expression vector pET28-TsMT3 was heterologously expressed in Escherichia coli to define the contribution of TsMT3 to heavy metal tolerance. In the presence of 2 mM CuSO4, 0.3 mM Pb(NO3)2 or 0.4 mM CdCl2, TsMT3 expressing cells exhibited enhanced metal tolerance and accumulated more metal than the controls. We believe that TsMT3 is probably involved in the processes of metal homeostasis, tolerance, and reactive oxygen species (ROS) scavenging.

Two types of aspartic proteinases from buckwheat seed--gene structure and expression analysis

Two types of aspartic proteinase (AP) genes have been isolated from the cDNA library of developing buckwheat seeds. Analysis of their sequences showed that one of these, FeAP9, resembled the structure and shared high homology with the so-called typical plant APs characterized by the presence of a plant-specific insert (PSI), an element unique among APs. The other cDNA, FeAPL1, encoded an AP-like protein lacking that domain. Different expression profiles were observed for FeAP9 and FeAPL1. FeAPL1 mRNAs were restricted to the seeds only, whereas FeAP9 mRNAs were also present in the other plant tissues - leaves, roots, and flowers. Higher levels of FeAP9 were observed in senescent leaves compared with green leaves. The differential expression pattern of these two unique APs raises the interesting possibility that these proteinases have unique substrate specificity and may have different roles in plant development and other physiological processes.

Two metallothionein gene family members in buckwheat: Expression analysis in flooding stress using Real Time RT-PCR technology

Metallothioneins (MTs) are an extensive and diverse family of small cysteine-rich proteins with metal-binding ability that are involved in metal homeostasis and detoxification. Two cDNA clones of the MT3 type, differing in 3? UTRs, were isolated from the developing buckwheat seed cDNA library. Following sequence analyses, expression profiles during flooding stress were monitored by Real Time RT PCR technology.

Functional analysis of the metallothionein gene cgMT1 isolated from the actinorhizal tree Casuarina glauca

cgMT1 is a metallothionein (MT)-like gene that was isolated from a cDNA library of young nitrogen-fixing nodules resulting from the symbiotic interaction between Frankia spp. and the actinorhizal tree Casuarina glauca. cgMT1 is highly transcribed in the lateral roots and nitrogen-fixing cells of actinorhizal nodules; it encodes a class I type 1 MT. To obtain insight into the function of cgMT1, we studied factors regulating the expression of the MT promoter region (PcgMT1) using a beta-glucuronidase (gus) fusion approach in transgenic plants of Arabidopsis thaliana. We found that copper, zinc, and cadmium ions had no significant effect on the regulation of PcgMT1-gus expression whereas wounding and H2O2 treatments led to an increase in reporter gene activity in transgenic leaves. Strong PcgMT1-gus expression also was observed when transgenic plants were inoculated with a virulent strain of the bacterial pathogen Xanthomonas campestris pv. campestris. Transgenic Arabidopsis plants expressing cgMT1 under the control of the constitutive 35S promoter were characterized by reduced accumulation of H2O2 when leaves were wounded and by increased susceptibility to the bacterial pathogen X. campestris. These results suggest that cgMT1 could play a role during the oxidative response linked to biotic and abiotic stresses.

High zinc concentrations reduce rooting capacity and alter metallothionein gene expression in white poplar (Populus alba L. cv. Villafranca)

Poplar is a good candidate for phytoremediation purposes because of its rapid growth, extensive root system, and ease of propagation and transformation; however its tolerance to heavy metals has not been fully investigated yet. In the present work, an in vitro model system with shoot cultures was used to investigate the tolerance to high concentrations of zinc (Zn) of a commercial clone (Villafranca) of Populus alba. Based on chlorophyll content (leaf chlorosis) and the rate of adventitious root formation from shoot cuttings as parameters of damage, 0.5-4mM zinc concentrations were all toxic albeit to different extents. Northern blot and reverse transcriptase (RT)-PCR analyses were used to examine the expression profiles of types 1, 2 and 3 PaMT genes in stems, leaves and roots of plants exposed to Zn treatments. In leaves, MT1 and MT3 mRNA levels were enhanced by Zn, while MT2 transcripts were not affected. The PaMT expression profiles were differentially affected by Zn in an organ-specific manner, and the relationship with Zn concentration and exposure time was rarely linear. The developmental and molecular data reveal that the in vitro model is a sensitive and reliable system to study heavy metal stress responses.

Zea mays L. protein changes in response to potassium dichromate treatments

The plant metabolic response to heavy metal stress is largely unknown. The present investigation was undertaken to examine the influence of different concentrations of potassium dichromate on the Zea mays L. plantlets. A clear effect of chromium on maize plantlets growth and seed germination was observed strating from 100-300 ppm up to 1500 ppm. In this concentration range, chromium uptake was dependent on the concentration in the medium. Metallothioneins, involved in heavy metal binding, were measured by capillary electrophoresis (CE), and showed a dose-response induction. Protein profile analyzed by two-dimensional gel electrophoresis showed differential expression of several proteins. Identification of spots of upregulated proteins was performed by MALDI mass spectrometry. Results showed that proteins induced by heavy metal exposure are principally involved in oxidative stress tolerance or in other stress pathways. Induction of proteins implicated in sugar metabolism was also observed. Identification of factors involved in plant response may lead to a better understanding of the mechanisms involved in cell protection and tolerance. This information could be used to improve agricultural production and environmental quality.

Plant metallothionein domains: functional insight into physiological metal binding and protein folding

Plant metallothioneins (MTs) differ from animal MTs by a peculiar sequence organization consisting of two short cysteine-rich terminal domains linked by a long cysteine-devoid spacer. The role of the plant MT domains in the protein structure and functionality is largely unknown. Here, we investigate the separate domain contribution to the in vivo binding of Zn and Cu and to confer metal tolerance to CUP1-null yeast cells of a plant type 2 MT (QsMT). For this purpose, we obtained three recombinant peptides that, respectively, correspond to the single N-terminal (N25) and C-terminal (C18) cysteine-rich domains of QsMT, and a chimera in which the spacer is replaced with a four-glycine bridge (N25-C18). The metal-peptide preparations recovered from Zn- or Cu-enriched cultures were characterized by ESI-MS, ICP-OES and CD and UV-vis spectroscopy and data compared to full length QsMT. Results are consistent with QsMT giving rise to homometallic Zn- or Cu-MT complexes according to a hairpin model in which the two Cys-rich domains interact to form a cluster. In this model the spacer region does not contribute to the metal coordination. However, our data from Zn-QsMT (but not from Cu-QsMT) support a fold of the spacer involving some interaction with the metal core. On the other hand, results from functional complementation assays in endogenous MT-defective yeast cells suggest that the spacer region may play a role in Cu-QsMT stability or subcellular localization. As a whole, our results provide the first insight into the structure/function relationship of plant MTs using the analysis of the separate domain abilities to bind physiological metals.