Bowman-birk proteinase inhibitor confers heavy metal and multiple drug tolerance in yeast

Cadmium-induced conformational changes in type 2 metallothionein of medicinal plant Coptis japonica: insights from molecular dynamics studies of apo, partially and fully metalated forms

Plants play an important role in the removal of excess heavy metals from soil and water. Medicinal plants can also have non-traditional use in phytoremediation technologies. Among the heavy metals, Cadmium (Cd) is the most abundant and readily taken up by the crop plants. Plant metallothioneins (MTs) are small proteins having cysteine-rich residues and appear to play key roles in metal homoeostasis. Plant metallothionein 2 (MT 2) from Coptis japonica (Gold-thread; CjMT 2) is a typical member of this subfamily and features two cysteine-rich regions containing eight and six cysteine residues, respectively, separated by 42 amino acids long linker region. In-silico analysis of MT 2 protein sequences of C. japonica was performed. In this study, ab initio methods were utilised for the prediction of three-dimensional structure of CjMT 2. After structure validation, heavy metal-binding sites were predicted for the selected modelled structures of CjMT 2. To obtain Cd_i-CjMT 2 (i = 1-7), metalated complex individual docking experiments were performed. The stability of the metalated docked structures was assessed by molecular dynamics (MD) simulation studies. Our study showed that CjMT 2 binds up to 4 Cd²⁺ ions in two distinct domains: a N-terminal β-domain that binds to 2 Cd²⁺ ions and a C-terminal α-domain that binds with 2 Cd²⁺ ions. Our analysis revealed that Cys residues of alpha and beta domain and some residues of spacer region of CjMT 2 protein might be important for the cadmium interaction. MD simulation studies provided insight into metal-induced conformational changes and mechanism of metalation of CjMT 2, an intrinsically disordered protein. This study provides useful insights into mechanism of cadmium-type 2 metallothionein interaction.

iTRAQ and virus-induced gene silencing revealed three proteins involved in cold response in bread wheat

By comparing the differentially accumulated proteins from the derivatives (UC 1110 × PI 610750) in the F₁₀ recombinant inbred line population which differed in cold-tolerance, altogether 223 proteins with significantly altered abundance were identified. The comparison of 10 cold-sensitive descendant lines with 10 cold-tolerant descendant lines identified 140 proteins that showed decreased protein abundance, such as the components of the photosynthesis apparatus and cell-wall metabolism. The identified proteins were classified into the following main groups: protein metabolism, stress/defense, carbohydrate metabolism, lipid metabolism, sulfur metabolism, nitrogen metabolism, RNA metabolism, energy production, cell-wall metabolism, membrane and transportation, and signal transduction. Results of quantitative real-time PCR of 20 differentially accumulated proteins indicated that the transcriptional expression patterns of 10 genes were consistent with their protein expression models. Virus-induced gene silencing of Hsp90, BBI, and REP14 genes indicated that virus-silenced plants subjected to cold stress had more severe drooping and wilting, an increased rate of relative electrolyte leakage, and reduced relative water content compared to viral control plants. Furthermore, ultrastructural changes of virus-silenced plants were destroyed more severely than those of viral control plants. These results indicate that Hsp90, BBI, and REP14 potentially play vital roles in conferring cold tolerance in bread wheat.

Resistance through inhibition: ectopic expression of serine protease inhibitor offers stress tolerance via delayed senescence in yeast cell

Protease inhibitors have been known to confer multiple stress tolerance in transgenic plants. We have assessed growth of yeast (Pichia pastoris GS115) strains expressing inhibitory repeat domains (PpIRD(+)) of previously characterized Capsicum annuum protease inhibitors under high salt, heavy metal and oxidative stress. PpIRD(+) strains exhibited multiple stress tolerance and showed differential molecular responses at transcriptional and translational level on exposure to stress inducing agents like heavy metal, high salt and H2O2. PpIRD(+) strains display significant reduction in metacaspase (Yca1) activity, the key enzyme in apoptosis, indicates the possibility of cross reactivity of IRDs (serine protease inhibitor) with cysteine proteases. PpIRD(+) and Saccharomyces cerevisiae knockout with Yca1 (ΔYca1) strain showed similar growth characteristics under stress, which indicated the delayed senescence due to cellular metacaspase inhibition. Molecular docking study showed a close proximity of IRDs reactive site and the active site of metacaspase in the complex that signified their strong interactions. Maintenance of GAPDH activity, primary target of metacaspase, in PpIRD(+) strain evidenced the inhibition of metacaspase activity and survival of these cells under stress. This report demonstrates a potential molecular mechanism of protease inhibitor-based multiple stress tolerance in yeast strains.

Characterization of a maize Wip1 promoter in transgenic plants

The Maize Wip1 gene encodes a wound-induced Bowman-Birk inhibitor (BBI) protein which is a type of serine protease inhibitor, and its expression is induced by wounding or infection, conferring resistance against pathogens and pests. In this study, the maize Wip1 promoter was isolated and its function was analyzed. Different truncated Wip1 promoters were fused upstream of the GUS reporter gene and transformed into Arabidopsis, tobacco and rice plants. We found that (1) several truncated maize Wip1 promoters led to strong GUS activities in both transgenic Arabidopsis and tobacco leaves, whereas low GUS activity was detected in transgenic rice leaves; (2) the Wip1 promoter was not wound-induced in transgenic tobacco leaves, but was induced by wounding in transgenic rice leaves; (3) the truncated Wip1 promoter had different activity in different organs of transgenic tobacco plants; (4) the transgenic plant leaves containing different truncated Wip1 promoters had low GUS transcripts, even though high GUS protein level and GUS activities were observed; (5) there was one transcription start site of Wip1 gene in maize and two transcription start sites of GUS in Wip1::GUS transgenic lines; (6) the adjacent 35S promoter which is present in the transformation vectors enhanced the activity of the truncated Wip1 promoters in transgenic tobacco leaves, but did not influence the disability of truncated Wip1231 promoter to respond to wounding signals. We speculate that an ACAAAA hexamer, several CAA trimers and several elements similar to ACAATTAC octamer in the 5'-untranslated region might contribute to the strong GUS activity in Wip1231 transgenic lines, meanwhile, compared to the 5'-untranslated region from Wip1231 transgenic lines, the additional upstream open reading frames (uORFs) in the 5'-untranslated region from Wip1737 transgenic lines might contribute to the lower level of GUS transcript and GUS activity.

Cloning, characterization and differential expression of a Bowman-Birk inhibitor during progressive water deficit and subsequent recovery in peanut (Arachis hypogaea) leaves

Bowman-Birk inhibitor (BBI) genes encode serine protease inhibitors well known for their anticarcinogenic properties and roles in plant defense against insects and pathogens. Here we investigated the expression of a BBI gene in response to water deficit, recovery and phytohormones. A full length cDNA encoding a novel BBI (AhBBI) was isolated from peanut (Arachis hypogaea L.) leaves. The deduced protein is a polypeptide of 11.5kDa containing a signal peptide of 20 amino acids which is missing from peanut seed full-length BBI. Sequence analysis showed that AhBBI presents the characteristic features of BBIs but its first inhibitory loop is unique among the Fabaceae species. Real-time PCR analyses indicated that in peanut leaves, AhBBI is upregulated by water deficit and exogenous jasmonic acid (JA) but repressed by abscissic acid (ABA) after 24h of treatment. The transcripts accumulation patterns during water deficit differed between two cultivars studied in relation to their tolerance levels to drought. AhBBI transcripts accumulated earlier and stronger in the tolerant cultivar (cv. Fleur11) compared to the susceptible one (cv. 73-30) suggesting that BBI genes are involved in drought stress tolerance. Subsequent rehydration reversed the accumulation of AhBBI transcripts in both cultivars but at different levels. The overall role of BBI in abiotic stress tolerance and the possible mechanisms of action are discussed.

Integration of molecular biology tools for identifying promoters and genes abundantly expressed in flowers of Oncidium Gower Ramsey

BACKGROUND

Orchids comprise one of the largest families of flowering plants and generate commercially important flowers. However, model plants, such as Arabidopsis thaliana do not contain all plant genes, and agronomic and horticulturally important genera and species must be individually studied.

RESULTS

Several molecular biology tools were used to isolate flower-specific gene promoters from Oncidium 'Gower Ramsey' (Onc. GR). A cDNA library of reproductive tissues was used to construct a microarray in order to compare gene expression in flowers and leaves. Five genes were highly expressed in flower tissues, and the subcellular locations of the corresponding proteins were identified using lip transient transformation with fluorescent protein-fusion constructs. BAC clones of the 5 genes, together with 7 previously published flower- and reproductive growth-specific genes in Onc. GR, were identified for cloning of their promoter regions. Interestingly, 3 of the 5 novel flower-abundant genes were putative trypsin inhibitor (TI) genes (OnTI1, OnTI2 and OnTI3), which were tandemly duplicated in the same BAC clone. Their promoters were identified using transient GUS reporter gene transformation and stable A. thaliana transformation analyses.

CONCLUSIONS

By combining cDNA microarray, BAC library, and bombardment assay techniques, we successfully identified flower-directed orchid genes and promoters.

Expression profiling of tobacco leaf trichomes identifies genes for biotic and abiotic stresses

Nicotiana tabacum (tobacco) plants have short and long glandular trichomes. There is evidence that tobacco trichomes play several roles in the defense against biotic and abiotic stresses. cDNA libraries were constructed from control and cadmium (Cd)-treated leaf trichomes. Almost 2,000 expressed sequence tag (EST) cDNA clones were sequenced to analyze gene expression in control and Cd-treated leaf trichomes. Genes for stress response as well as for primary metabolism scored highly, indicating that the trichome is a biologically active and stress-responsive tissue. Reverse transcription-PCR (RT-PCR) analysis demonstrated that antipathogenic T-phylloplanin-like proteins, glutathione peroxidase and several classes of pathogenesis-related (PR) proteins were expressed specifically or dominantly in trichomes. Cysteine-rich PR proteins, such as non-specific lipid transfer proteins (nsLTPs) and metallocarboxypeptidase inhibitors, are candidates for the sequestration of metals. The expression of osmotin and thaumatin-like proteins was induced by Cd treatment in both leaves and trichomes. Confocal laser scanning microscopy (CLSM) showed that glutathione levels in tip cells of both long and short trichomes were higher than those in other types of leaf cells, indicating the presence of an active sulfur-dependent protective system in trichomes. Our results revealed that the trichome-specific transcriptome approach is a powerful tool to investigate the defensive functions of trichomes against both abiotic and biotic stress. Trichomes are shown to be an enriched source of useful genes for molecular breeding towards stress-tolerant plants.

A novel plant cysteine-rich peptide family conferring cadmium tolerance to yeast and plants

We have identified a novel cDNA clone, termed DcCDT1, from Digitaria ciliaris, that confers cadmium (Cd)-tolerance to yeast (Saccharomyces cerevisiae). The gene encodes a predicted peptide of 55 amino acid residues of which 15 (27.3%) are cysteine residues. We found that monocotyledonous plants possess multiple DcCDT1 homologues, for example rice contains five DcCDT1 homologues (designated OsCDT1~5), whereas dicotyledonous plants, including Arabidopsis thaliana, Brassica rapa, poplar (Populus tremula x Populus alba) and Picea sitchensis, appear to possess only a single homologue. GFP fusion experiments demonstrate that DcCDT1 and OsCDT1 are targeted to both the plant cytoplasmic membranes and cell walls. Constitutive expression of DcCDT1 or OsCDT1 confers Cd-tolerance to transgenic A. thaliana plants by lowering the accumulation of Cd in the cells. The functions of the DcCDT1 family members are discussed in the light of these findings.

Novel cysteine-rich peptides from Digitaria ciliaris and Oryza sativa enhance tolerance to cadmium by limiting its cellular accumulation

By means of functional screening using the cadmium (Cd)-sensitive ycf1 yeast mutant, we have isolated a novel cDNA clone, DcCDT1, from Digitaria ciliaris growing in a former mining area in northern Japan, and have shown that it confers Cd tolerance to the yeast cells, which accumulated almost 2-fold lower Cd levels than control cells. The 521 bp DcCDT1 cDNA contains an open reading frame of 168 bp and encodes a deduced peptide, DcCDT1, that is 55 amino acid residues in length, of which 15 (27.3%) are cysteine residues. Five DcCDT1 homologs (here termed OsCDT1-OsCDT5) have been identified in rice, and all of them were up-regulated to varying degrees in the above-ground tissues by CdCl(2) treatment. Localization of green fluorescent protein fusions suggests that DcCDT1 and OsCDT1 are targeted to both cytoplasmic membranes and cell walls of plant cells. Transgenic Arabidopsis thaliana plants overexpressing DcCDT1 or OsCDT1 displayed a Cd-tolerant phenotype and, consistent with our yeast data, accumulated lower amounts of Cd when grown on CdCl(2). Collectively, our data suggest that DcCDT1 and OsCDT1 function to prevent entry of Cd into yeast and plant cells and thereby enhance their Cd tolerance.

A Bowman-Birk type protease inhibitor is involved in the tolerance to salt stress in wheat

A salt-responsive gene WRSI5 was characterized from salt-tolerant cultivar Shanrong No. 3 (SR3), an introgression line via asymmetric somatic hybrid between Triticum aestivum L. cv. Jinan177 (JN177) and Thinopyrum ponticum Podp. The peptide encoded by WRSI5 contains a Bowman-Birk domain sharing a high level of sequence identity to monocotyledonous protease inhibitors. When expressed in vitro, the WRSI5 gene product exhibited trypsin, but not chymotrypsin inhibition. The expression level of WRSI5 was increased in SR3 roots exposed to salt, drought or oxidative stress. In situ hybridization showed that it is induced in the endodermal cells of the mature region of the SR3 root tip, with no signal detectable in the corresponding region of the salt-susceptible cultivar JN177. SR3 has a higher selectivity for K(+) over Na(+), and therefore limits the transport of Na(+) from the root to the shoot. When overexpressed in Arabidopsis thaliana, WRSI5 improves the ability of seedlings to grow on a medium containing 150 mM NaCl. We suggest that WRSI5 plays an important role in regulating the plant growth rate or long-distance Na(+) transport in SR3 plants exposed to salt stress.

Galactinol synthase gene of Coptis japonica is involved in berberine tolerance

Many plant secondary metabolites show strong biological activities and are potentially also toxic to plants, while plants producing such active compounds are usually insensitive to their own metabolites, suggesting that they have species-specific detoxification mechanisms. In order to clarify the detoxification mechanism of alkaloids, we used cultured cells of Coptis japonica, which are capable of producing a yellow benzylisoquinoline alkaloid, berberine, and accumulate it in the vacuole. Unlike other plant cells that do not produce berberine, C. japonica shows strong tolerance to this alkaloid. We established a fission yeast strain that was sensitive to berberine and performed functional screening using a C. japonica cDNA library. One cDNA clone, which conferred clear berberine tolerance, encoded galactinol synthase (CjGolS). The possible role of CjGolS in berberine tolerance is discussed.