Molecular characterization of gene sequences coding for protein disulfide isomerase (PDI) in durum wheat (Triticum turgidum ssp. durum)

PDI-Regulated Disulfide Bond Formation in Protein Folding and Biomolecular Assembly

Disulfide bonds play a pivotal role in maintaining the natural structures of proteins to ensure their performance of normal biological functions. Moreover, biological molecular assembly, such as the gluten network, is also largely dependent on the intermolecular crosslinking via disulfide bonds. In eukaryotes, the formation and rearrangement of most intra- and intermolecular disulfide bonds in the endoplasmic reticulum (ER) are mediated by protein disulfide isomerases (PDIs), which consist of multiple thioredoxin-like domains. These domains assist correct folding of proteins, as well as effectively prevent the aggregation of misfolded ones. Protein misfolding often leads to the formation of pathological protein aggregations that cause many diseases. On the other hand, glutenin aggregation and subsequent crosslinking are required for the formation of a rheologically dominating gluten network. Herein, the mechanism of PDI-regulated disulfide bond formation is important for understanding not only protein folding and associated diseases, but also the formation of functional biomolecular assembly. This review systematically illustrated the process of human protein disulfide isomerase (hPDI) mediated disulfide bond formation and complemented this with the current mechanism of wheat protein disulfide isomerase (wPDI) catalyzed formation of gluten networks.

"Expression of genes encoding protein disulfide isomerase (PDI) in cultivars and lines of common wheat with different baking quality of flour"

BACKGROUND

The subject of this research was to investigate the level of expression of genes encoding protein disulfide isomerase (PDI) in cultivars and lines of wheat with different baking value of flour. PDI plays a key role in the formation of disulfide bonds in newly formed proteins. Each of cultivars and lines had a specific set of high molecular weight glutenin subunits (HMW-GS). Based on the presence of individual subunits, the potential baking value is predicted. Sometimes this value is not confirmed during technological analysis. Since there are cases where flour has a better or worse value than expected on the basis of the genotype, the expression of PDI genes was considered as a potential cause for discrepancies mentioned.

RESULTS

Analysis focused on three stages of grain development. The expression level of PDI genes was compared between wheat cultivars and lines with different genotype-phenotype combinations, which means diversified sets of HMW-GS combined with diversified qualitative classification. The highest expression level of PDI was noticed at early stage of grain development, which is consistent with the function of PDI. The expression level was evaluated by the real-time PCR technique.

CONCLUSION

Results obtained in this work did not allow for a clear statement of decisive significance of PDI in the context of shaping the final baking value. The results of this work contribute to an ever more in-depth understanding of the mechanisms governing baking value, and thus to the progress of the selection of new varieties with more beneficial properties.

On the interactions among zinc availability and responses to ozone stress in durum wheat seedlings

Seedlings of durum wheat [Triticum turgidum subsp. durum (Desf.) Husn] were exposed to zinc nutrition and to ozone (O₃) in a factorial combination: adequate (+Zn treatment) or no Zn (-Zn) in the nutrient solution, followed by exposure to either ozone-free air (filtered air, FA) or to 150 nL L^-1 ozone (O₃) for 4 h. Although omitting Zn from the nutrient solution failed to impose a genuine Zn deficiency, -Zn*FA durum wheat seedlings showed a typical deficiency behaviour, i.e. Zn mobilisation from root to shoot. Such inter-organ Zn redistribution, however, did not occur in -Zn*O₃ plants. Exposure to each stress singly decreased the activity and the protein amount of foliar plasma membrane H⁺-ATPase, but not stress combination, which even increased the H⁺-ATPase expression with respect to control. In the -Zn*O₃ plants, moreover, the foliar activities of the plasma membrane-bound NAD(P)H-dependent superoxide synthase and of Cu,Zn-superoxide dismutase, and the transcripts abundance of the luminal binding protein and of the protein disulphide isomerase, were also stimulated. It is proposed that, even in the absence of actual Zn starvation, the perception of deficiency conditions could trigger changes in redox homoeostasis at the plasma membrane level, helpful in compensating an O₃-dependent oxidative damage.

A disulphide isomerase gene (PDI-V) from Haynaldia villosa contributes to powdery mildew resistance in common wheat

In this study, we report the contribution of a PDI-like gene from wheat wild relative Haynaldia villosa in combating powdery mildew. PDI-V protein contains two conserved thioredoxin (TRX) active domains (a and a′) and an inactive domain (b). PDI-V interacted with E3 ligase CMPG1-V protein, which is a positive regulator of powdery mildew response. PDI-V was mono-ubiquitinated by CMPG1-V without degradation being detected. PDI-V was located on H. villosa chromosome 5V and encoded for a protein located in the endoplasmic reticulum. Bgt infection in leaves of H. villosa induced PDI-V expression. Virus induced gene silencing of PDIs in a T. durum-H. villosa amphiploid compromised the resistance. Single cell transient over-expression of PDI-V or a truncated version containing the active TXR domain a decreased the haustorial index in moderately susceptible wheat cultivar Yangmai 158. Stable transgenic lines over-expressing PDI-V in Yangmai 158 displayed improved powdery mildew resistance at both the seedling and adult stages. By contrast over-expression of point-mutated PDI-V^C57A did not increase the level of resistance in Yangmai 158. The above results indicate a pivotal role of PDI-V in powdery mildew resistance and showed that conserved TRX domain a is critical for its function.

Expression and characterization of protein disulfide isomerase family proteins in bread wheat

BACKGROUND

The major wheat seed proteins are storage proteins that are synthesized in the rough endoplasmic reticulum (ER) of starchy endosperm cells. Many of these proteins have intra- and intermolecular disulfide bonds. In eukaryotes, the formation of most intramolecular disulfide bonds in the ER is thought to be catalyzed by protein disulfide isomerase (PDI) family proteins. The cDNAs that encode eight groups of bread wheat (Triticum aestivum L.) PDI family proteins have been cloned, and their expression levels in developing wheat grains have been determined. The purpose of the present study was to characterize the enzymatic properties of the wheat PDI family proteins and clarify their expression patterns in wheat caryopses.

RESULTS

PDI family cDNAs, which are categorized into group I (TaPDIL1Aα, TaPDIL1Aβ, TaPDIL1Aγ, TaPDIL1Aδ, and TaPDIL1B), group II (TaPDIL2), group III (TaPDIL3A), group IV (TaPDIL4D), and group V (TaPDIL5A), were cloned. The expression levels of recombinant TaPDIL1Aα, TaPDIL1B, TaPDIL2, TaPDIL3A, TaPDIL4D, and TaPDIL5A in Escherichia coli were established from the cloned cDNAs. All recombinant proteins were expressed in soluble forms and purified. Aside from TaPDIL3A, the recombinant proteins exhibited oxidative refolding activity on reduced and denatured ribonuclease A. Five groups of PDI family proteins were distributed throughout wheat caryopses, and expression levels of these proteins were higher during grain filling than in the late stage of maturing. Localization of these proteins in the ER was confirmed by fluorescent immunostaining of the immature caryopses. In mature grains, the five groups of PDI family proteins remained in the aleurone cells and the protein matrix of the starchy endosperm.

CONCLUSIONS

High expression of PDI family proteins during grain filling in the starchy endosperm suggest that these proteins play an important role in forming intramolecular disulfide bonds in seed storage proteins. In addition, these PDI family proteins that remain in the aleurone layers of mature grains likely assist in folding newly synthesized hydrolytic enzymes during germination.

The Rad50 genes of diploid and polyploid wheat species. Analysis of homologue and homoeologue expression and interactions with Mre11

The MRN complex plays a central role in the DNA repair pathways of eukaryotic cells and takes part in many other processes, including cell cycle checkpoint signalling, meiosis, DNA replication and telomere maintenance. This complex is formed by the interaction of the products of the Mre11, Rad50 and Nbs1 genes. This paper reports the molecular characterization, expression and interactions of the Rad50 gene in several wheat species with different levels of ploidy. The homoeologous Rad50 wheat genes were found to show a high level of conservation. Most of the RAD50 domains and motifs previously described in other species were also present in wheat RAD50; these proteins are therefore likely to have similar functions. Interactions between the RAD50 wheat proteins and their MRE11 counterparts in the MRN complex were observed. The level of expression of Rad50 in each of the species examined was determined and compared with those previously reported for the Mre11 genes. In some cases similar levels of expression were seen, as expected. The expression of the RAD50 homoeologous genes was assessed in two polyploid wheat species using quantitative PCR. In both cases, an overexpression of the Rad50B gene was detected. Although the results indicate the maintenance of function of these species' three homoeologous Rad50 genes, the biased expression of Rad50B might indicate ongoing silencing of one or both other homoeologues in polyploid wheat. To assess the consequences of such silencing on the formation of the MRN complex, the interactions between individual homoeologues of Rad50 and their genomic counterpart Mre11 genes were examined. The results indicate the inexistence of genomic specificity in the interactions between these genes. This would guarantee the formation of an MRN complex in wheat.

Gene networks in the synthesis and deposition of protein polymers during grain development of wheat

As the amino acid storing organelle, the protein bodies provide nutrients for embryo development, seed germination and early seedling growth through storage proteolysis in cereal plants, such as wheat and rice. In protein bodies, the monomeric and polymeric prolamins, i.e. gliadins and glutenins, form gluten and play a key role in determining dough functionality and end-product quality of wheat. The formation of intra- and intermolecular bonds, including disulphide and tyrosine bonds, in and between prolamins confers cohesivity, viscosity, elasticity and extensibility to wheat dough during mixing and processing. In this review, we summarize recent progress in wheat gluten research with a focus on the fundamental molecular biological aspects, including transcriptional regulation on genes coding for prolamin components, biosynthesis, deposition and secretion of protein polymers, formation of protein bodies, genetic control of seed storage proteins, the transportation of the protein bodies and key enzymes for determining the formation of disulphide bonds of prolamin polymers.

The Protein Disulfide Isomerase gene family in bread wheat (T. aestivum L.)

BACKGROUND

The Protein Disulfide Isomerase (PDI) gene family encodes several PDI and PDI-like proteins containing thioredoxin domains and controlling diversified metabolic functions, including disulfide bond formation and isomerisation during protein folding. Genomic, cDNA and promoter sequences of the three homologous wheat genes encoding the "typical" PDI had been cloned and characterized in a previous work. The purpose of present research was the cloning and characterization of the complete set of genes encoding PDI and PDI like proteins in bread wheat (Triticum aestivum cv Chinese Spring) and the comparison of their sequence, structure and expression with homologous genes from other plant species.

RESULTS

Eight new non-homologous wheat genes were cloned and characterized. The nine PDI and PDI-like sequences of wheat were located in chromosome regions syntenic to those in rice and assigned to eight plant phylogenetic groups. The nine wheat genes differed in their sequences, genomic organization as well as in the domain composition and architecture of their deduced proteins; conversely each of them showed high structural conservation with genes from other plant species in the same phylogenetic group. The extensive quantitative RT-PCR analysis of the nine genes in a set of 23 wheat samples, including tissues and developmental stages, showed their constitutive, even though highly variable expression.

CONCLUSIONS

The nine wheat genes showed high diversity, while the members of each phylogenetic group were highly conserved even between taxonomically distant plant species like the moss Physcomitrella patens. Although constitutively expressed the nine wheat genes were characterized by different expression profiles reflecting their different genomic organization, protein domain architecture and probably promoter sequences; the high conservation among species indicated the ancient origin and diversification of the still evolving gene family. The comprehensive structural and expression characterization of the complete set of PDI and PDI-like wheat genes represents a basis for the functional characterization of this gene family in the hexaploid context of bread wheat.

Identification and validation of reference genes for quantitative RT-PCR normalization in wheat

BACKGROUND

Usually the reference genes used in gene expression analysis have been chosen for their known or suspected housekeeping roles, however the variation observed in most of them hinders their effective use. The assessed lack of validated reference genes emphasizes the importance of a systematic study for their identification. For selecting candidate reference genes we have developed a simple in silico method based on the data publicly available in the wheat databases Unigene and TIGR.

RESULTS

The expression stability of 32 genes was assessed by qRT-PCR using a set of cDNAs from 24 different plant samples, which included different tissues, developmental stages and temperature stresses. The selected sequences included 12 well-known HKGs representing different functional classes and 20 genes novel with reference to the normalization issue. The expression stability of the 32 candidate genes was tested by the computer programs geNorm and NormFinder using five different data-sets. Some discrepancies were detected in the ranking of the candidate reference genes, but there was substantial agreement between the groups of genes with the most and least stable expression. Three new identified reference genes appear more effective than the well-known and frequently used HKGs to normalize gene expression in wheat. Finally, the expression study of a gene encoding a PDI-like protein showed that its correct evaluation relies on the adoption of suitable normalization genes and can be negatively affected by the use of traditional HKGs with unstable expression, such as actin and alpha-tubulin.

CONCLUSION

The present research represents the first wide screening aimed to the identification of reference genes and of the corresponding primer pairs specifically designed for gene expression studies in wheat, in particular for qRT-PCR analyses. Several of the new identified reference genes outperformed the traditional HKGs in terms of expression stability under all the tested conditions. The new reference genes will enable more accurate normalization and quantification of gene expression in wheat and will be helpful for designing primer pairs targeting orthologous genes in other plant species.

Molecular cloning and characterization of two soybean protein disulfide isomerases as molecular chaperones for seed storage proteins

Protein disulfide isomerase family proteins play important roles in the folding of nascent polypeptides and the formation of disulfide bonds in the endoplasmic reticulum. In this study, we cloned two similar protein disulfide isomerase family genes from soybean leaf (Glycine max L. Merrill. cv Jack). The cDNAs encode proteins of 525 and 551 amino acids, named GmPDIL-1 and GmPDIL-2, respectively. Recombinant versions of GmPDIL-1 and GmPDIL-2 expressed in Escherichia coli exhibited oxidative refolding activity for denatured RNaseA. Genomic sequences of both GmPDIL-1 and GmPDIL-2 were cloned and sequenced. The comparison of soybean genomic sequences with those of Arabidopsis, rice and wheat showed impressive conservation of exon-intron structure across plant species. The promoter sequences of GmPDIL-1 apparently contain a cis-acting regulatory element functionally linked to unfolded protein response. GmPDIL-1, but not GmPDIL-2, expression was induced under endoplasmic reticulum-stress conditions. GmPDIL-1 and GmPDIL-2 promoters contain some predicted regulatory motifs for seed-specific expression. Both proteins were ubiquitously expressed in soybean tissues, including cotyledon, and localized to the endoplasmic reticulum. Data from coimmunoprecipitation experiments suggested that GmPDIL-1 and GmPDIL-2 associate with proglycinin, a precursor of the seed storage protein glycinin, and the alpha'-subunit of beta-conglycinin, a seed storage protein found in cotyledon cells under conditions that disrupt the folding of glycinin or beta-conglycinin, suggesting that GmPDIL-1 and GmPDIL-2 are involved in the proper folding or quality control of such storage proteins as molecular chaperones.

Molecular and phylogenetic analysis of MADS-box genes of MIKC type and chromosome location of SEP-like genes in wheat (Triticum aestivum L.)

Transcription factors encoded by MIKC-type MADS-box genes control many important functions in plants, including flower development and morphogenesis. The cloning and characterization of 45 MIKC-type MADS-box full-length cDNA sequences of common wheat is reported in the present paper. Wheat EST databases were searched by known sequences of MIKC-type genes and primers were designed for cDNA cloning by RT-PCR. Full-length cDNAs were obtained by 5' and 3' RACE extension. Southern analysis showed that three copies of the MIKC sequences, corresponding to the three homoeologous genes, were present. This genome organization was further confirmed by aneuploid analysis of six SEP-like genes, each showing three copies located in different homoeologous chromosomes. Phylogenetic analysis included the wheat MIKC cDNAs into 11 of the 13 MIKC subclasses identified in plants and corresponding to most genes controlling the floral homeotic functions. The expression patterns of the cDNAs corresponding to different homeotic classes was analysed in 18 wheat tissues and floral organs by RT-PCR, real time RT-PCR and northern hybridisation. Potential functions of the genes corresponding to the cloned wheat cDNAs were predicted on the basis of sequence homology and comparable expression pattern with functionally characterized MADS-box genes from Arabidopsis and monocot species.

The Inhibitory Effects of Coumarin on the Germination of Durum Wheat (Triticum turgidum ssp. durum, cv. Simeto) Seeds

The event chain leading to germination blockage in durum wheat (Triticum turgidum ssp. durum Desf.) seeds exposed to the allelochemical coumarin (2H-chromen-2-one) was studied. The physiological and biochemical aspects thought to be critical for a successful seed germination were measured. At concentrations above 200 microM: , coumarin inhibited seed germination in a concentration-dependent manner. Inhibition occurred early during seed imbibition (phase I), was rapid, and irreversible. During phase I, coumarin inhibited water uptake, electrolyte retention capacity, and O(2) consumption. Later on, coumarin delayed the reactivation of peroxidases, enhanced the activity of superoxide dismutase, decreased the activities of selected marker enzymes for metabolic resumption, and repressed the transcription of molecular chaperones involved in secretory pathways. Insufficient and/or late seed rehydration caused by coumarin could have delayed membrane stabilization or decreased respiratory O(2) consumption, both of which are conducive to an overproduction of reactive O(2) species. Being unbalanced by an adequate upsurge of antioxidant defense systems, the resulting oxidative stress might have ultimately interfered with the germination program.

Cloning and characterization of wheat PDI (protein disulfide isomerase) homoeologous genes and promoter sequences

The genomic and cDNA sequences of three PDI homoeologous genes located on chromosomes 4A, 4B and 4D of bread wheat and their promoters were cloned and sequenced. The three sequences showed a very high conservation of the coding region and of the exon/intron structure, which consisted of ten exons. The comparison of wheat sequences with those of rice and Arabidopsis showed a significant conservation of the exon/intron structure across the three species. The expression of each gene was analysed by RT-PCR in different plant tissues (roots, coleoptiles, spikelets, leaves and developing caryopses). All the genes showed a higher expression in developing caryopses than in other analysed tissues, wherein some differences were detected. The promoter sequences of the three genes possessed some regulatory motifs typical of endosperm specific expression.

The PDI genes of wheat and their syntenic relationship to the esp2 locus of rice

The storage protein polymers in the endosperm, stabilised by disulphide bonds, determine a number of processing qualities of wheat dough. The enzyme protein disulphide isomerase (PDI), involved in the formation of disulphide bonds, is strongly suggested to play a role in the formation of wheat storage protein bodies. Reports of the rice mutant esp2 exhibiting aberrant storage protein deposition in conjunction with a lack of PDI expression provided strong indications of a direct role for PDI in storage protein deposition. The potential significance of wheat PDI prompted the present studies into exploring any orthology between wheat PDI genes and rice PDI and esp2 loci. By designing allele-specific (AS)-polymerase chain reaction (PCR) markers, two of the three wheat PDI genes could be genetically mapped to group 4 chromosomes and showed close association with GERMIN genes. Physical mapping led to localisation of wheat PDI genes to chromosomal "bins" on the proximal section of chromosome 4AL and distal sections of 4BS and 4DS. Identification of the putative PDI gene of rice and its comparison to the esp2 locus revealed that they were present at similar positions on the short arm of chromosome 11. Analysis of a large section of the PDI-containing section of rice chromosome 11S revealed a number of putative orthologues from The Institute for Genomic Research Triticum aestivum Gene Index database, of which five had been mapped, each localising to group 4 chromosomes, many in good agreement with our mapping results. The results strongly suggest a close linkage between the esp2 marker and the PDI gene of rice and an orthology between the PDI loci of rice and wheat and predict quantitative-trait loci involved in storage protein deposition at the PDI loci.

Specific patterns of changes in wheat gene expression after treatment with three antifungal compounds

The two fungicides azoxystrobin and fenpropimorph are used against powdery mildew and rust diseases in wheat (Triticum aestivumL). Azoxystrobin, a strobilurin, inhibits fungal mitochondrial respiration and fenpropimorph, a morpholin, represses biosynthesis of ergosterol, the major sterol of fungal membranes. Although the fungitoxic activity of these compounds is well understood, their effects on plant metabolism remain unclear. In contrast to the fungicides which directly affect pathogen metabolism, benzo(1,2,3) thiadiazole-7-carbothioic acid S-methylester (BTH) induces resistance against wheat pathogens by the activation of systemic acquired resistance in the host plant. In this study, we monitored gene expression in spring wheat after treatment with each of these agrochemicals in a greenhouse trial using a microarray containing 600 barley cDNA clones. Defence-related genes were strongly induced after treatment with BTH, confirming the activation of a similar set of genes as in dicot plants following salicylic acid treatment. A similar gene expression pattern was observed after treatment with fenpropimorph and some defence-related genes were induced by azoxystrobin, demonstrating that these fungicides also activate a defence reaction. However, less intense responses were triggered than with BTH. The same experiments performed under field conditions gave dramatically different results. No gene showed differential expression after treatment and defence genes were already expressed at a high level before application of the agrochemicals. These differences in the expression patterns between the two environments demonstrate the importance of plant growth conditions for testing the impact of agrochemicals on plant metabolism.

Detection and relative quantitation of Soil-borne cereal mosaic virus (SBCMV) and Polymyxa graminis in winter wheat using real-time PCR (TaqMan®)

Soil-borne cereal mosaic virus (SBCMV) was first reported affecting wheat crops in Italy in 1960 and has spread subsequently to many other European countries, including the UK. SBCMV causes a serious disease of wheat, reducing yield by up to 70%; growing resistant varieties represents the only economical means of control. Real-time RT-PCR and PCR assays based on TaqMan chemistry were developed for the detection and quantitation of SBCMV and its vector, Polymyxa graminis. Each assay incorporated an RNA or DNA specific internal control to facilitate quantitation. Nucleic acid extracts from SBCMV-infected plants were diluted in a nucleic acid extract from a healthy plant and amplified by real-time PCR to produce a standard curve. The standard curve was used to quantify the amount of SBCMV and P. graminis in plant samples. The sensitivity of the real-time assays were compared to established serological quantitation and conventional PCR methods by testing a range of SBCMV-infected wheat varieties. The results indicate that real-time assays were a 1000 times more sensitive than ELISA for the quantitation of SBCMV, and a 100 times more sensitive than conventional PCR for the quantitation of P. graminis. Real-time assays enabled sensitive, reproducible and specific detection of both virus and vector in wheat tissues. The real-time assays are potentially useful tools for determining variations in virus and vector concentrations in plant tissue from wheat varieties differing in resistance to SBCMV.

Oxidative Folding of Amaranthus α-Amylase Inhibitor

Oxidative folding is the fusion of native disulfide bond formation with conformational folding. This complex process is guided by two types of interactions: first, covalent interactions between cysteine residues, which transform into native disulfide bridges, and second, non-covalent interactions giving rise to secondary and tertiary protein structure. The aim of this work is to understand both types of interactions in the oxidative folding of Amaranthus alpha-amylase inhibitor (AAI) by providing information both at the level of individual disulfide species and at the level of amino acid residue conformation. The cystine-knot disulfides of AAI protein are stabilized in an interdependent manner, and the oxidative folding is characterized by a high heterogeneity of one-, two-, and three-disulfide intermediates. The formation of the most abundant species, the main folding intermediate, is favored over other species even in the absence of non-covalent sequential preferences. Time-resolved NMR and photochemically induced dynamic nuclear polarization spectroscopies were used to follow the oxidative folding at the level of amino acid residue conformation. Because this is the first time that a complete oxidative folding process has been monitored with these two techniques, their results were compared with those obtained at the level of an individual disulfide species. The techniques proved to be valuable for the study of conformational developments and aromatic accessibility changes along oxidative folding pathways. A detailed picture of the oxidative folding of AAI provides a model study that combines different biochemical and biophysical techniques for a fuller understanding of a complex process.

Thioredoxins and related proteins in photosynthetic organisms: molecular basis for thiol dependent regulation

Thioredoxins are small molecular weight disulfide oxidoreductases specialized in the reduction of disulfide bonds on other proteins. Generally, the enzymes which are selectively and reversibly reduced by these proteins oscillate between an oxidized and inactive conformation and a reduced and active conformation. Thioredoxin constitutes the archetype of a family of protein disulfide oxidoreductases which comprises glutaredoxin and protein disulfide isomerase. Thioredoxin and glutaredoxin serve many roles in the cell, including the redox regulation of target enzymes and transcription factors. They can also serve as hydrogen donors to peroxiredoxins, recently discovered heme free peroxidases, the function of which is to get rid of hydroperoxides in the cell. This review describes the molecular basis for the functioning and interaction between these enzymes in photosynthetic organisms.

Molecular characterization of a novel protein disulfide isomerase in carrot

A protein disulfide isomerase (PDI) coding sequence was cloned from a cDNA library derived from carrot (Daucus carota L.) somatic embryos. The cDNA is 2060 bp in length and encodes for a protein of 581 amino acids and molecular weight of 64.4 kDa. Primary structure analysis of the deduced protein revealed two thioredoxin-like active sites and an endoplasmic reticulum-retention signal at its C-terminus, which is also found in PDIs in plants and animals. Although between the carrot protein and other plant PDIs there is only about 30% identity, the active site regions are almost identical. The corresponding mRNA was found in varying amounts, in all tissues investigated. A recombinant protein expressed from the carrot cDNA clone effectively catalyzed both glutathione-insulin transhydrogenation and the oxidative renaturation of denatured RNase A. These results suggest that the protein coded for by the carrot gene is a novel member of the PDI family in plants. We therefore designated this novel carrot gene PDIL1. The protein expressed by the PDIL1 cDNA sequence had a highly acidic stretch at its N-terminal region (no such domain exists in known plant PDIs), and was located far from known plant PDIs on a maximum likelihood tree. The PDIL1 gene, together with closely-related genes identified in Arabidopsis and tomato, was suggested to belong to a novel subfamily of PDIs.

Molecular characterization of a Bombyx mori protein disulfide isomerase (bPDI)

We have isolated a complementary deoxyribonucleic acid clone that encodes the protein disulfide isomerase of Bombyx mori (bPDI). This protein has a putative open reading frame of 494 amino acids and a predicted size of 55.6 kDa. In addition, 2 thioredoxin active sites, each with a CGHC sequence, and an endoplasmic reticulum (ER) retention signal site with a KDEL motif were found at the C-terminal. Both sites are typically found in members of the PDI family of proteins. The expression of bPDI messenger ribonucleic acid (mRNA) was markedly increased during ER stress induced by stimulation with calcium ionophore A23187, tunicamycin, and dithiothreitol, all of which are known to cause an accumulation of unfolded proteins in the ER. We also examined the tissue distribution of bPDI mRNA and found pronounced expression in the fat body of insects. Hormonal regulation studies showed that juvenile hormone, insulin, and a combination of juvenile hormone and transferrin (although not transferrin alone) affected bPDI mRNA expression. A challenge with exogenous bacteria also affected expression, and the effect peaked 16 hours after infection. These results suggest that bPDI is a member of the ER-stress protein group, that it may play an important role in exogenous bacterial infection of the fat body, and that its expression is hormone regulated.