Soyacystatin, a novel cysteine proteinase inhibitor in soybean, is distinct in protein structure and gene organization from other cystatins of animal and plant origin

Genome-Wide Identification and Characterization of the Cystatin Gene Family in Bread Wheat (Triticum aestivum L.)

Cystatins, as reversible inhibitors of papain-like and legumain proteases, have been identified in several plant species. Although the cystatin family plays crucial roles in plant development and defense responses to various stresses, this family in wheat (Triticum aestivum L.) is still poorly understood. In this study, 55 wheat cystatins (TaCystatins) were identified. All TaCystatins were divided into three groups and both the conserved gene structures and peptide motifs were relatively conserved within each group. Homoeolog analysis suggested that both homoeolog retention percentage and gene duplications contributed to the abundance of the TaCystatin family. Analysis of duplication events confirmed that segmental duplications played an important role in the duplication patterns. The results of codon usage pattern analysis showed that TaCystatins had evident codon usage bias, which was mainly affected by mutation pressure. TaCystatins may be regulated by cis-acting elements, especially abscisic acid and methyl jasmonate responsive elements. In addition, the expression of all selected TaCystatins was significantly changed following viral infection and cold stress, suggesting potential roles in response to biotic and abiotic challenges. Overall, our work provides new insights into TaCystatins during wheat evolution and will help further research to decipher the roles of TaCystatins under diverse stress conditions.

Sugarcane cystatins: From discovery to biotechnological applications

Phytocystatins are tight-binding cysteine protease inhibitors produced by plants. The first phytocystatin described was isolated from Oryza sativa and, since then, cystatins from several plant species were reported, including from sugarcane. Sugarcane cystatins were unraveled in Sugarcane EST project database, after sequencing of cDNA libraries from various sugarcane tissues at different developmental stages and six sugarcane cystatins were cloned, expressed and characterized (CaneCPI-1 to CaneCPI-6). These recombinant proteins were produced in different expression systems and inhibited several cysteine proteases, including human cathepsins B and L, which can be involved in pathologies, such as cancer. In this review, we summarize a comprehensive history of all sugarcane cystatins, presenting an updated phylogenetic analysis; chromosomal localization, and genomic organization. We also present protein docking of CaneCPI-5 in the active site of human cathepsin B, insights about canecystatins structures; recombinant expression in different systems, comparison of their inhibitory activities against human cysteine cathepsins B, K, L, S, V, falcipains from Plasmodium falciparum and a cathepsin L-like from the sugarcane weevil Sphenophorus levis; and enlighten their potential and current applications in agriculture and health.

A new Piper nigrum cysteine proteinase inhibitor, PnCPI, with antifungal activity: molecular cloning, recombinant expression, functional analyses and molecular modeling

A new Piper nigrum cysteine proteinase inhibitor, PnCPI, belonging to group I of phytocystatins, with inhibitory activity against papain and growth of Fusarium solani f. sp. piperis, was isolated and characterized. Previous studies (de Souza et al. 2011) have identified a partial cDNA sequence of putative cysteine proteinase inhibitor differentially expressed in roots of black pepper (P. nigrum L.) infected by F. solani f. sp. piperis. Here, we aimed to isolate the full-length cDNA and genomic sequences of the P. nigrum cysteine proteinase inhibitor gene, named PnCPI. Sequence analyses showed that the PnCPI gene encodes a deduced protein of 108 amino acid residues with a predicted molecular mass of 12.3 kDa and isoelectric point of 6.51. Besides the LARFAV-like sequence, common to all phytocystatins, PnCPI contains three conserved motifs of the superfamily cystatin: a glycine residue at the N-terminal region, the QxVxG reactive site more centrally positioned, and one tryptophan in the C-terminal region. PnCPI, belonging to group I of phytocystatins, showed high identity with cystatins isolated from several plant species. Sequence analyses also revealed no putative signal peptide at the N-terminal of PnCPI, as well as no introns within the genomic sequence corresponding to the PnCPI coding region. Molecular modeling showed the ability of PnCPI to interact with papain, while its inhibitory activity against this protease was confirmed after heterologous expression in Escherichia coli. The effects of heat treatments on the inhibitory activity of recombinant PnCPI, rPnCPI, were evaluated. In addition, rPnCPI exhibited in vitro activity against F. solani f. sp. piperis, revealing a new cystatin with the potential antifungal application. The identification of PnCPI as a functional cystatin able to inhibit the in vitro growth of F. solani f. sp. piperis indicates other factors contributing to in vivo susceptibility of black pepper to root rot disease.

Recombinant expression, characterization and phylogenetic studies of novels cystatins-like proteins of sweet orange (Citrus sinensis) and clementine (Citrus clementina)

Phytocystatins are plant cystatins that are related to several physiological processes regulating endogenous cysteine proteases involved in seed development and germination, programmed cell death and response to stress conditions. In addition, phytocystatins can act in plant defense against exogenous peptidases from herbivorous insects, pathogens and nematodes. Considering that Citrus fruits are important to human nutrition and represent a high value crop in worldwide agriculture, in the present work, we performed the identification of putative cystatins from Citrus sinensis and from Citrus clementine and submitted them to phylogenetic analysis. Six cystatins from each species were identified as orthologous and classified into three well supported phylogenetic groups. Five cystatins representative of the phylogenetic groups were recombinantly expressed and the in vitro studies revealed them to be potent inhibitors against the cysteine peptidases papain, legumain, human cathepsins (B, L, S, K) and a cathepsin B-like from Diaphorina citri (the Asian Citrus psyllid). Our findings provide the C. clementina and C. sinensis cystatins classification and an enzyme-inhibitor interactions profile, which may reflect an evolutionary process of Citrus cystatins related to gene functions as initial germination rates and seedlings development as well associated to plant defense against pathogens, as insects and nematodes.

Phytocystatins and their Potential Application in the Development of Drought Tolerance Plants in Soybeans (Glycine max L.)

Plant cystatins, also called phytocystatins constitute a family of specific cysteine protease inhibitors found in several monocots and dicots. In soybean, phytocystatins regulate several endogenous processes contributing immensely to this crop's tolerance to abiotic stress factors. Soybeans offer numerous nutritional, pharmaceutical and industrial benefits; however, their growth and yields is hampered by drought, which causes more than 10% yield losses recorded every harvest period worldwide. This review analyses the role of papain-like cysteine proteases and their inhibitors in soybean plant growth and development under drought stress. It also describes their localisation, regulation, target organs and tissues, and the overall impact of cystatins on generating drought tolerance soybean plants. These proteins have many functions that remain poorly characterized, particularly under abiotic stress. Although much information is available on the utilisation of proteases for industrial applications, very few reports have focused on the impact of proteases on plant stress responses. The exploitation of cystatins in plant engineering, as competitive proteases inhibitors is one of the means that will guarantee the continued utilisation of soybeans as an important oilseed crop.

ClCPI, a cysteine protease inhibitor purified from Cassia leiandra seeds has antifungal activity against Candida tropicalis by inducing disruption of the cell surface

Infections caused by Candida tropicalis have increased significantly worldwide in parallel with resistance to antifungal drugs. To overcome resistance novel drugs have to be discovered. The objective of this work was to purify and characterize a cysteine protease inhibitor from the seeds of the Amazon rainforest tree Cassia leiandra and test its inhibitory effect against C. tropicalis growth. The inhibitor, named ClCPI, was purified after ion exchange and affinity chromatography followed by ultrafiltration. ClCPI is composed of a single polypeptide chain and is not a glycoprotein. The molecular mass determined by SDS-PAGE in the absence or presence of β-mercaptoethanol and ESI-MS were 16.63 kDa and 18.362 kDa, respectively. ClCPI was stable in the pH range of 7.0-9.0 and thermostable up to 60 °C for 20 min. ClCPI inhibited cysteine proteases, but not trypsin, chymotrypsin neither alpha-amylase. Inhibition of papain was uncompetitive with a Ki of 4.1 × 10^-7 M and IC₅₀ of 8.5 × 10^-7 M. ClCPI at 2.6 × 10^-6 M reduced 50% C. tropicalis growth. ClCPI induced damages and morphological alterations in C. tropicalis cell surface, which led to death. These results suggest that ClCPI have great potential for the development of an antifungal drug against C. tropicalis.

Food functionality research as a new national project in special reference to improvement of cognitive and locomotive abilities

In Japan, where a super-aging society is realized, we are most concerned about healthy longevity, which would ascertain the wellness of people by improving their quality of life (QOL). In 2014, the Cabinet Office proposed a strategic innovation promotion programme, launching a national project for the development of the agricultural-forestry-fisheries food products with new functionalities for the next generation. In addition to focusing on a conventional prevention of lifestyle-associated metabolic syndromes, the project targets the scientific evidence of the activation of brain cognitive ability and the improvement of bodily locomotive function. The project also involves the analysis of the foods-sports interrelation of chronic importance, and the development of devices for the verification of QOL-associated maintenance of homeostasis. In this review, we provide an overview of these studies, with special reference to cognition as a case of the gut-brain axis which the author is particularly interested in.

Molecular Cloning, Recombinant Expression and Antifungal Activity of BnCPI, a Cystatin in Ramie (Boehmeria nivea L.)

Phytocystatins play multiple roles in plant growth, development and resistance to pests and other environmental stresses. A ramie (Boehmeria nivea L.) phytocystatin gene, designated as BnCPI, was isolated from a ramie cDNA library and its full-length cDNA was obtained by rapid amplification of cDNA ends (RACE). The full-length cDNA sequence (691 bp) consisted of a 303 bp open reading frame (ORF) encoding a protein of 100 amino acids with deduced molecular mass of 11.06 kDa and a theoretical isoelectric point (pI) of 6.0. The alignment of genome DNA (accession No. MF153097) and cDNA sequences of BnCPI showed that an intron (~104 bp) exists in the coding region. The BnCPI protein contains most of the highly conserved blocks including Gly⁵-Gly⁶ at the N-terminal, the reactive site motif QxVxG (Q⁴⁹V⁵⁰V⁵¹S⁵²G⁵³), the L⁷⁹-W⁸⁰ block and the [LVI]-[AGT]-[RKE]-[FY]-[AS]-[VI]-x-[EDQV]-[HYFQ]-N (L²²G²³R²⁴ F²⁵A²⁶V²⁷ D²⁸D²⁹H³⁰ N³¹) block that is common among plant cystatins. BLAST analysis indicated that BnCPI is similar to cystatins from Glycine max (77%), Glycine soja (76%), Hevea brasiliensis (75%) and Ricinus communis (75%). The BnCPI was subcloned into expression vector pSmart-I and then overexpressed in Escherichia coli BL21 (DE3) as a His-tagged recombinant protein. The purified reBnCPI has a molecular mass of 11.4 kDa determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS–PAGE). Purified reBnCPI can efficiently inhibit the protease activity of papain and ficin toward BANA (Nα-benzoyl-L-arginine-2-naphthyamide), as well as the mycelium growth of some important plant pathogenic fungi. The data further contribute to our understanding of the molecular functions of BnCPI.

Molecular Characterization and Expression Profiling of Brachypodium distachyon L. Cystatin Genes Reveal High Evolutionary Conservation and Functional Divergence in Response to Abiotic Stress

Cystatin is a class of proteins mainly involved in cysteine protease inhibition and plant growth and development, as well as tolerance under various abiotic stresses. In this study, we performed the first comprehensive analysis of the molecular characterization and expression profiling in response to various abiotic stresses of the cystatin gene family in Brachypodium distachyon, a novel model plant for Triticum species with huge genomes. Comprehensive searches of the Brachypodium genome database identified 25 B. distachyon cystatin (BdC) genes that are distributed unevenly on chromosomes; of these, nine and two were involved in tandem and segmental duplication events, respectively. All BdC genes had similar exon/intron structural organization, with three conserved motifs similar to those from other plant species, indicating their high evolutionary conservation. Expression profiling of 10 typical BdC genes revealed ubiquitous expression in different organs at varying expression levels. BdC gene expression in seedling leaves was particularly highly induced by various abiotic stresses, including the plant hormone abscisic acid and various environmental cues (cold, H₂O₂, CdCl₂, salt, and drought). Interestingly, most BdC genes were significantly upregulated under multiple abiotic stresses, including BdC15 under all stresses, BdC7-2 and BdC10 under five stresses, and BdC7-1, BdC2-1, BdC14, and BdC12 under four stresses. The putative metabolic pathways of cytastin genes in response to various abiotic stresses mainly involve the aberrant protein degradation pathway and reactive oxygen species (ROS)-triggered programmed cell death signaling pathways. These observations provide a better understanding of the structural and functional characteristics of the plant cystatin gene family.

Purification and biochemical characterization of phytocystatin from Brassica alba

Phytocystatins belong to the family of cysteine proteinases inhibitors. They are ubiquitously found in plants and carry out various significant physiological functions. These plant derived inhibitors are gaining wide consideration as potential candidate in engineering transgenic crops and in drug designing. Hence it is crucial to identify these inhibitors from various plant sources. In the present study a phytocystatin has been isolated and purified by a simple two-step procedure using ammonium sulfate saturation and gel filtration chromatography on Sephacryl S-100HR from Brassica alba seeds (yellow mustard seeds).The protein was purified to homogeneity with 60.3% yield and 180-fold of purification. The molecular mass of the mustard seed cystatin was estimated to be nearly 26,000 Da by sodium dodecyl sulfate polyacrylamide gel electrophoresis as well as by gel filtration chromatography. The stokes radius and diffusion coefficient of the mustard cystatin were found to be 23A° and 9.4 × 10(-7)  cm(2) s(-1) respectively. The isolated phytocystatin was found to be stable in the pH range of 6-8 and is thermostable up to 60 °C. Kinetic analysis revealed that the phytocystatin exhibited non-competitive type of inhibition and inhibited papain more efficiently (K(i)  = 3 × 10(-7)  M) than ficin (K(i)  = 6.6 × 10(-7)  M) and bromelain (K(i) = 7.7 × 10(-7)  M respectively). CD spectral analysis shows that it possesses 17.11% alpha helical content.

Functional characterization of the N-terminal and C-terminal domains of a sesame group II phytocystatin

BACKGROUND

Phytocystatins are natural inhibitors of cysteine protease, and may regulate endo- or exo-genous proteolytic activities in plants. They are classified into Group I and II differing by the presence of C-terminal extension of Group II. A cDNA fragment encoding a Group II phytosystatin, SiCYS was previously obtained from sesame seeds.

RESULTS

SiCYS as well as its two structural domains, N-terminal and C-terminal domains (SiCYS-N and SiCYS-C), was expressed in Escherichia coli. The recombinant SiCYS and SiCYS-N showed inhibitory activity against papain. The K i values of SiCYS and SiCYS-N were ~1.9 ×10^-8 M and ~7.9 ×10^-8 M, respectively. All the three recombinants possessed comparable ability to inhibit spore germination of Trichoderma reesei, Aspergillus sydowii, and Helminthosporium sesamum. Similar protein profile including proteases in germinating seeds was found in proteins purified by the SiCYS, SiCYS-N or SiCYS-C coupling affinity column.

CONCLUSION

SiCYS exhibited more effective papain-inhibitory activity than SiCYS-N; while SiCYS-C had almost no inhibitory activity. All displayed similar antifungal activities indicating that there is no correlation between antifungal and papain-inhibitory activities. Structural and sequence analyses suggest that the C-terminal domain of SiCYS may be originated from gene duplication to enhance its inhibitory activity.

Comprehensive analysis of cystatin family genes suggests their putative functions in sexual reproduction, embryogenesis, and seed formation

Cystatins are tightly bound and reversible inhibitors of cysteine proteases in C1A and C13 peptidase families, which have been identified in several species and shown to function in vegetative development and response to biotic/abiotic stresses in plants. Recent work revealed their critical role in regulating programmed cell death during embryogenesis in tobacco and suggested their more comprehensive roles in the process of sexual plant reproduction, although little is known about cystatin family genes in the processes. Here, 10 cystatin family genes in Nicotiana tabacum were identified using an expressed sequence tag (EST)-based gene clone strategy. Analysis of their biochemical properties showed that nine of them have the potency to inhibit the activities of both commercial cathepsin L-like proteases and extracted cysteine proteases from seeds, but with different K i values depending on the types of proteases and the developmental stages of the seed tested. This suggests that cystatin-dependent cathepsin L-like proteolytic pathways are probably important for early seed development. Comprehensive expression profile analysis revealed that cystatin family genes showed manifold variations in their transcription levels in different plant cell types, including the sperm, egg, and zygote, especially in the embryo and seed at different developmental stages. More interestingly, intracellular localization analysis of each cystatin revealed that most members of cystatin families are recognized as secretory proteins with signal peptides that direct them to the endoplasmic reticulum. These results suggest their widespread roles in cell fate determination and cell-cell communication in the process of sexual reproduction, especially in gamete and embryo development, as well as in seed formation.

Biochemical and immunological characterization of a recombinantly-produced antifungal cysteine proteinase inhibitor from green kiwifruit (Actinidia deliciosa)

Plant proteinase inhibitors are considered important defense molecules against insect and pathogen attack. The cysteine proteinase inhibitor (CPI) from green kiwifruit (Actinidia deliciosa) belongs to the cystatin family and shows potent antifungal activity (in vitro and in vivo). However, the low abundance of this molecule in fruit (6μg/g of fresh fruit) seems to limit further investigations on the interaction between phytocystatin and photopathogenic fungi. In this paper the cDNA of the kiwi CPI was expressed in Escherichia coli. Fifteen N-terminal amino acids were identified by Edman degradation, and 77% of the rCPI primary structure was confirmed by mass fingerprint. The structural homology of recombinant CPI (rCPI) to its natural counterpart has been clearly demonstrated in immunological assays (immunoblot and ELISA inhibition). Biological activity of rCPI was demonstrated in inhibition assay with cysteine proteinase papain (EC50 2.78nM). In addition, rCPI reveals antifungal properties toward pathogenic fungi (Alternaria radicina and Botrytis cinerea), which designates it as an interesting model protein for the exploration of plant phytocystatins - pathogen interactions. Understanding the molecular mechanisms of natural plant resistance could lead to the development of ecologically safe fungicides for controlling post-harvest diseases and maintaining food quality.

Heterologous expression of corn cystatin in soybean and effect on growth of the stink bug

The bean bug (Riptortus clavatus) is a serious insect pest of soybean. Corn (maize) cystatin strongly inhibited the activity of its digestive cysteine proteinase. Heterologous expression of corn cystatin in soybean seeds inhibited the insect's proteases, but not its growth.

A physiologically regulated multidomain cystatin of wheat shows stage-dependent immunity against Karnal Bunt (Tilletia indica)

To identify novel components of basal resistance against the Tellitia indica of wheat, breeding for disease resistance was carried out on resistant and susceptible genotype of Karnal Bunt. The different members of wheat cystatin gene families were cloned, and their role in triggering differential resistance through co-expression was analyzed in our lab. The multidomain wheat cystatin (WCM) is a proteinase inhibitor characterized by cloning the gene from susceptible (WH542) and resistant genotype (HD 29). A WCM cDNA was isolated from both genotypes and sequenced. The WCM had a highly conserved N-terminal cystatin domain and a long C-terminal extension containing a second region, which exhibited similarity to the cystatin domain. The expression level was significantly (P > 0.001) higher in resistant compared to susceptible genotype at all the physiological stages of wheat spikes. In order to characterize the biochemical properties of WCM, the coding sequence was expressed in Escherichia coli using pET expression vector. The recombinant WCM was purified from soluble fraction of the cell extract by using affinity chromatography. WCM, with 23 KDa molecular mass, showed cysteine proteinase inhibitory activity against papain (Ki 3.039 × 10(-7) M) as determined by using BAPNA as substrate. Furthermore, it was able to arrest the fungal mycelial growth of T. indica. Hyphae growth was inhibited, and morphological changes such as swelling and fragmentation of the fungus were observed. Overall, these observations suggest an endogenous high expression of cystatin, possibly associated with the resistance of wheat against Karnal bunt.

Abnormally high digestive enzyme activity and gene expression explain the contemporary evolution of a Diabrotica biotype able to feed on soybeans

Western corn rootworm (Diabrotica virgifera) (WCR) depends on the continuous availability of corn. Broad adoption of annual crop rotation between corn (Zea mays) and nonhost soybean (Glycine max) exploited WCR biology to provide excellent WCR control, but this practice dramatically reduced landscape heterogeneity in East-central Illinois and imposed intense selection pressure. This selection resulted in behavioral changes and “rotation-resistant” (RR) WCR adults. Although soybeans are well defended against Coleopteran insects by cysteine protease inhibitors, RR-WCR feed on soybean foliage and remain long enough to deposit eggs that will hatch the following spring and larvae will feed on roots of planted corn. Other than documenting changes in insect mobility and egg laying behavior, 15 years of research have failed to identify any diagnostic differences between wild-type (WT)- and RR-WCR or a mechanism that allows for prolonged RR-WCR feeding and survival in soybean fields. We documented differences in behavior, physiology, digestive protease activity (threefold to fourfold increases), and protease gene expression in the gut of RR-WCR adults. Our data suggest that higher constitutive activity levels of cathepsin L are part of the mechanism that enables populations of WCR to circumvent soybean defenses, and thus, crop rotation. These new insights into the mechanism of WCR tolerance of soybean herbivory transcend the issue of RR-WCR diagnostics and management to link changes in insect gut proteolytic activity and behavior with landscape heterogeneity. The RR-WCR illustrates how agro-ecological factors can affect the evolution of insects in human-altered ecosystems.

Molecular analysis of maize cystatin expression as fusion product in Escherichia coli

Nowadays, plant cysteine proteinase inhibitors "namely phytocystatins" have attracted researchers towards the identification of their molecular structures and novel physiological functions. Their important roles in plant developmental processes and different stress responses have been well known. In spite of advances in the understanding of phytocystatins, we lack enough data concerning their heterologous expression especially in the forms of fusion products that are most important whether for biochemical, pharmacological or clinical studies. The present work describes an easy method of expression, purification and functional characterization in Escherichia coli of maize cystatin as a part of maltose-binding fusion protein. Assessments revealed that upon expression of fused product the total antioxidation status of the induced recombinant cells is increased. This result leads to question 'Is there any parallel functional correlation between anti-proteolytic and anti-oxidative systems?' However, the present research will open a gate for the new studies regarding the putative communicative roles of these systems that may be existing in the biological world.

Molecular cloning and biochemical characterization of a novel cystatin from Hevea rubber latex

A novel cDNA encoding a cysteine proteinase inhibitor or phytocystatin was isolated from Hevea brasiliensis RRIM600 rubber latex cDNA library. The full-length HbCPI obtained from rapid amplification of cDNA ends contains 588 bp. An open reading frame of 306 bp encodes for a protein of 101 amino acids with the typical inhibitory motifs of phytocystatin superfamily, namely the central signature motif QXVXG, a GG doublet and LARFAV-like motifs in the N-terminal part, and conserved A/PW residues in the C-terminal region. Sequence comparison showed that the deduced amino acid sequence was similar to that of cysteine protease inhibitor from Manihot esculenta (84% identity). The HbCPI was subcloned into expression vector pQE-40 and then overexpressed in Escherichia coli M15 strain (pREP4) as a His-tagged recombinant protein with molecular mass approximately 13 kDa. The purified HbCPI showed thermal stable property and efficiently inhibited the protease activity of papain by non-competitive inhibition with K(i) value of 15.4 nM. Beside latex, HbCPI also transcripted in leaf and young seed. The HbCPI message accumulation was induced by phytopathogenic fungi Phytophthora palmivora infection. These data suggest that HbCPI might play crucial roles in defense mechanism against biotic stimuli.

In search of decoy/guardee to R genes: deciphering the role of sugars in defense against Fusarium wilt in chickpea

Plant responses are coordinately controlled by both external and internal signals. Apt perception of pathogen attack and its appropriate conversion to internal signals ultimately determine the outcome of innate immunity. The present review predicts the involvement of unconventional 'Guard/Decoy Model' in chickpea-Fusarium encounter. Rapid alkalinization factor is predicted to act as initial 'Gatekeeper decoy' counteracting fungal entry. Phospholipases and cystatins probably function as 'Guardees' being shielded by R gene(s). Serine Threonine Kinases decodes external pathogenic signals to in planta defense alarms. 14.3.3 provides clues to the wilt mechanism. The versatile sugars serve as signal generators and transmitters maintaining intra and inter cellular connectivity during stress.

Distinct expression patterns of two Arabidopsis phytocystatin genes, AtCYS1 and AtCYS2, during development and abiotic stresses

The phytocystatins of plants are members of the cystatin superfamily of proteins, which are potent inhibitors of cysteine proteases. The Arabidopsis genome encodes seven phytocystatin isoforms (AtCYSs) in two distantly related AtCYS gene clusters. We selected AtCYS1 and AtCYS2 as representatives for each cluster and then generated transgenic plants expressing the GUS reporter gene under the control of each gene promoter. These plants were used to examine AtCYS expression at various stages of plant development and in response to abiotic stresses. Histochemical analysis of AtCYS1 promoter- and AtCYS2 promoter-GUS transgenic plants revealed that these genes have similar but distinct spatial and temporal expression patterns during normal development. In particular, AtCYS1 was preferentially expressed in the vascular tissue of all organs, whereas AtCYS2 was expressed in trichomes and guard cells in young leaves, caps of roots, and in connecting regions of the immature anthers and filaments and the style and stigma in flowers. In addition, each AtCYS gene has a unique expression profile during abiotic stresses. High temperature and wounding stress enhanced the expression of both AtCYS1 and AtCYS2, but the temporal and spatial patterns of induction differed. From these data, we propose that these two AtCYS genes play important, but distinct, roles in plant development and stress responses.

Molecular cloning and characterization of novel cystatin gene in leaves Cakile maritima halophyte

Cakile maritima (Brassicaceae) is a halophyte that thrives on dunes along Mediterranean seashores, with high tolerance to salty and dry environments. We have previously shown that there is great morphological and physiological diversity between ecotypes. We investigated the expression of cysteine protease inhibitor (cystatin) genes in the response to hydric and saline constraints, as cystatins are known to participate in the response to environmental constraints in plants. We isolated, from C. maritime, a new cystatin cDNA (CmC) that encodes a 221 amino acid protein with a calculated molecular mass of 25 kDa. It displays a moderate-to-high amino acid sequence similarity with previously reported phytocystatin genes. The predicted protein is hydrophilic, with only one hydrophobic region, just at its N-terminus, and a calculated isoelectric point of 6.7. Sequence analysis revealed a monocystatin structure with one cystatin-like domain. The predicted protein CmC contains the main conserved motifs characteristic of the plant cystatins, and a putative site of phosphorylation by casein kinase II (TPSD). As some cystatins, it contains a C-terminal extension of 106 amino acid residues, with several conserved cystatin motifs. The expression was constitutive in non-stressed plants, with different levels between the ecotypes, and without apparent relation to the climatic area of origin. Augmented expression was observed under severe salinity except in the ecotype from the arid region. Water deficit also increased CmC expression in two ecotypes, with the highest value observed in the ecotype from the humid region. These results indicate that C. maritima responds to high salinity and water deficit by expressing a cystatin gene that is a known component of defense against abiotic constraints or biotic aggression and survival machinery.

Characterization of inhibitory mechanism and antifungal activity between group-1 and group-2 phytocystatins from taro (Colocasia esculenta)

Tarocystatin from Colocasia esculenta, a group-2 phytocystatin, is a defense protein against phytopathogenic nematodes and fungi. It is composed of a highly conserved N-terminal region, which is homological to group-1 cystatin, and a repetitive peptide at the C-terminus. The purified recombinant proteins of tarocystatin, such as full-length (FL), N-terminus (Nt) and C-terminus (Ct) peptides, were produced and their inhibitory activities against papain as well as their antifungal effects were investigated. Kinetic analysis revealed that FL peptide exhibited mixed type inhibition (K(ia) = 0.098 microM and K(ib) = 0.252 microM) and Nt peptide showed competitive inhibition (K(i) = 0.057 microM), whereas Ct peptide possessed weak papain activation properties. A shift in the inhibitory pattern from competitive inhibition of Nt peptide alone to mixed type inhibition of FL peptide implied that the Ct peptide has an regulatory effect on the function of FL peptide. Based on the inhibitory kinetics of FL (group-2) and Nt (group-1) peptides on papain activity, an inhibitory mechanism of group-2 phytocystatins and a regulatory mechanism of extended Ct peptide have each been proposed. By contrast, the antifungal activity of Nt peptide appeared to be greater than that of FL peptide, and the Ct peptide showed no effect on antifungal activity, indicating that the antifungal effect is not related to proteinase inhibitory activity. The results are valid for most phytocystatins with respect to the inhibitory mechanism against cysteine proteinase.

Identification of Cysteine Proteases and Screening of Cysteine Protease Inhibitors in Biological Samples by a Two-Dimensional Gel System of Zymography and Reverse Zymography

We have developed a two-dimensional (2D-) gel system of zymography and reverse zymography for the detection and characterization of proteases and protease inhibitors. Isoelectric focusing (IEF) agarose gels with pH gradients were employed for separation in the first-dimension and sodium dodecyl sulfate (SDS)-polyacrylamide gel copolymerized with gelatin used for the second dimension. Proteases and protease inhibitors separated by IEF gel were applied on the second gel without trichloroacetic acid (TCA) fixation. Protease activity in the 2D-gel was visualized as transparent spots where gelatin substrate was digested after commassie brilliant blue (CBB) staining. Some of the transparent spots from the skin mucus extract of rainbow trout were determined to be a cysteine protease through use of E-64 or CA-074. In the reverse zymography technique, the gel was incubated with papain solution at 37°C for 18 h. Cysteine protease inhibitors from broad bean seeds were detected as clear blue spots after CBB staining. The amino (N-) terminal sequences of four papain inhibitor spots thus detected were demonstrated to be identical to that of favin β chain, a broad bean lectin. Taken together, our system can be considered to be an efficient technique for discovering and characterizing new proteases and protease inhibitors in biological samples. This is the first report describing a 2D-gel system of zymography and reverse zymography.

Cloning of a cDNA encoding a cystatin from grain amaranth (Amaranthus hypochondriacus) showing a tissue-specific expression that is modified by germination and abiotic stress

A cDNA, encoding a cysteine protease inhibitor (AhCPI), was isolated from an immature seed cDNA library of grain amaranth (Amaranthus hypochondriacus L.) and characterized. It encoded a polypeptide of 247 amino acids (aa), including a putative N-terminal signal peptide. Other relevant regions found in its sequence included the G and PW conserved aa motifs, the consensus LARFAV sequence for phytocystatins and the reactive site QVVAG. The predicted aa sequence for AhCPI showed a significant homology to other plant cystatins. Gene expression analyses indicated that AhCPI was constitutively expressed in mature seeds, and gradually decreased during germination. In vegetative tissues, AhCPI was expressed in the radicle and hypocotyls of seedlings and in the stems and roots of young plantlets. Its expression in roots and stems increased substantially in response to water deficit, salinity-, cold- and heat-stress, whereas heat-stress induced a rapid and transient accumulation of AhCPI transcripts in leaves. The results obtained were suggestive of multiple roles for AhCPI in grain amaranth, acting as a regulator of seed germination and as a protective agent against diverse types of abiotic stress, which induced this gene in a tissue- and stress-specific manner. The work herewith described reports a novel, and apparently, single cystatin protein in which, in agreement with other plant model systems, could have a regulatory role in germination, and further expands previous findings linking the accumulation of protease inhibitors, mostly of the serine proteinase type, with protection against (a)biotic stress in A. hypochondriacus.

MsCYS1, a developmentally-regulated cystatin from alfalfa

Several roles have been attributed to cystatins in plants, ranging from the regulation of host [endogenous] cysteine proteases to the inhibition of herbivorous pest [exogenous] proteases. We report here the cloning, expression and functional characterization of a novel cystatin from alfalfa, Medicago sativa L. The new sequence, isolated from a cDNA expression library prepared from young leaves, encodes a protein, MsCYS1, with the typical inhibitory motifs of cystatins, namely the central signature motif QxVxG, a GG doublet in the N-terminal trunk, and a W residue in the C-terminal region, about 30 amino acids distant from the central inhibitory motif. As shown by a protein-based phylogenetic reconstruction, MsCYS1 is a close relative of other cystatins from Fabaceae presumably involved in the regulation of endogenous proteases. This cystatin is developmentally regulated in stems and leaves, and not induced by stress signals including methyl jasmonate, known to activate cystatins involved in plant defense. A recombinant form of MsCYS1 expressed in Escherichia coli was shown to strongly inhibit alfalfa leaf cysteine proteases while showing weak affinity for the digestive cysteine proteases of different herbivorous pests. Overall, these observations suggest an endogenous protease regulatory role for MsCYS1, possibly associated with the early development of stems and leaves.

Carboxy terminal extended phytocystatins are bifunctional inhibitors of papain and legumain cysteine proteinases

Plant legumains are cysteine proteinases putatively involved in processing endogenous proteins. Phytocystatins (PhyCys) have been described as plant inhibitors of papain-like cysteine proteinases. Some PhyCys contain a carboxy terminal extension with an amino acid motif (SNSL) similar to that involved in the inhibition of legumain-like proteins by human cystatins. The role of these carboxy terminal extended PhyCys as inhibitors of legumain-like cysteine proteinases is here shown by in vitro inhibition of human legumain and legumain-like activities from barley extracts. Moreover, site-directed mutagenesis has demonstrated that the asparagine of the SNSL motif is essential in this inhibition. We prove for first time the existence of legumain inhibitors in plants.

A multicomponent, elicitor-inducible cystatin complex in tomato, Solanum lycopersicum

We assessed the ability of the fungal elicitor arachidonic acid to induce cystatin genes in tomato (Solanum lycopersicum), using a cDNA expression library from arachidonate-treated leaves. The cDNAs of two novel cystatins were isolated, coding for an approx. 11-kDa protein, SlCYS10; and for a 23.6-kDa protein, SlCYS9, bearing an N-terminal signal peptide and a long, 11.5-kDa extension at the C terminus. Both genes were induced by arachidonate but not by methyl jasmonate, an inducer of the 88-kDa eight-unit cystatin, multicystatin, accumulated in the cytosol of leaf cells upon herbivory. A truncated form of SlCYS9, tSlCYS9, was produced by deletion of the C-terminal extension to assess the influence of this structural element on the cystatin moiety. As shown by kinetic and stability assays with recombinant variants expressed in Escherichia coli, deleting the extension influenced both the overall stability and inhibitory potency of SlCYS9 against cysteine proteases of herbivorous organisms. These findings provide evidence for a multicomponent elicitor-inducible cystatin complex in tomato, including at least 10 cystatin units produced via two metabolic routes.

Molecular modeling and inhibitory activity of cowpea cystatin against bean bruchid pests

Plant cystatins show great potential as tools to genetically engineer resistance of crop plants against pests. Two important potential targets are the bean weevils Acanthoscelides obtectus and Zabrotes subfasciatus, which display major activities of digestive cysteine proteinases in midguts. In this study a cowpea cystatin, a cysteine proteinase inhibitor found in cowpea (Vigna unguiculata) seeds, was expressed in Escherichia coli and purified with a Ni-NTA agarose column. It strongly inhibited papain and proteinases from midguts of both A. obtectus and Z. subfasciatus bruchids, as seen by in vitro assays. When the protein was incorporated into artificial seeds at concentrations as low as 0.025%, and seeds were consumed by the bruchids larva, dramatic reductions in larval weight, and increases in insect mortality were observed. Molecular modeling studies of cowpea cystatin in complex with papain revealed that five N-terminal residues responsible for a large proportion of the hydrophobic interactions involved in the stabilization of the enzyme-inhibitor complex are absent in the partial N-terminal amino acid sequencing of soybean cystatin. We suggest that this structural difference could be the reason for the much higher effectiveness of cowpea cystatin when compared to that previously tested phytocystatin. The application of this knowledge in plant protein mutation programs aiming at enhancement of plant defenses to pests is discussed.

A cold inducible multidomain cystatin from winter wheat inhibits growth of the snow mold fungus, Microdochium nivale

A novel cold-induced cystatin cDNA clone (TaMDC1) was isolated from cold acclimated winter wheat crown tissue by using a macroarray-based differential screening method. The deduced amino acid sequence consisted of a putative N-terminal secretory signal peptide of 37 amino acids and a mature protein (mTaMDC1) with a molecular mass of 23 kDa. The mTaMDC1 had a highly conserved N-terminal cystatin domain and a long C-terminal extension containing a second region, which exhibited partial similarity to the cystatin domain. The recombinant mTaMDC1 was purified from Escherichia coli and its cysteine proteinase inhibitory activity against papain was analyzed. The calculated Ki value of 5.8 x 10(-7) M is comparable to those reported for other phytocystatins. Northern and western blot analyses showed elevated expression of TaMDC1 mRNA and protein during cold acclimation of wheat. In addition to cold, accumulation of the TaMDC1 message was induced by other abiotic stresses including drought, salt and ABA treatment. Investigation of in vitro antifungal activity of mTaMDC1 showed strong inhibition on the mycelium growth of the snow mold fungus Microdochium nivale. Hyphae growth was totally inhibited in the presence of 50 mug/ml mTaMDC1 and morphological changes such as swelling, fragmentation and sporulation of the fungus were observed. The mechanisms of the in vitro antifungal effects and the possible involvement of TaMDC1 in cold induced snow mold resistance of winter wheat are discussed.

Studies on low molecular mass phytocystatins purified from Phaseolus mungo (Urd)

In the present study two phytocystatins (thiol protease inhibitors) have been isolated and purified to homogeneity from Phaseolus mungo by a simple two-step procedure using ammonium sulfate fractionation and gel filtration on Sephacryl-100 HR. The latter procedure yielded two peaks of the inhibitors (PMC I and PMC II). The pH optimum of both phytocystatins was pH 7.0; the temperature optima for PMC I and PMC II were 65 and 70 degrees C, respectively. The molecular masses of the purified phytocystatins were 19 and 17 kD, respectively, as determined by SDS-PAGE and mass spectrometry. Antibodies raised against the purified cystatins gave a single precipitin line in Ouchterlony double immunodiffusion. Kinetics of inhibition showed that PMC I and PMC II strongly inhibit papain and ficin but not trypsin and chymotrypsin. Binding stoichiometry of PMC I and PMC II with both papain and ficin was 1 : 2. The effect of urea on PMC I and PMC II was analyzed by fluorescence and circular dichroism spectroscopy. The CD results suggest an unfolding of PMC I and PMC II accompanying a decrease in the amount of extended (hydrated) coil structure and an increase in sheet-like structure. FTIR results show that PMC I is structurally similar to PMC II. Hydrophobic interactions are observed over a long time scale (5-150 min). Furthermore, fluorescence spectroscopy results were found to be in accordance with CD results, by showing quenching of fluorescence intensity of PMC I and PMC II, although to different extents, due to perturbations of the environment of aromatic residues in the protein. Both cystatins showed strong inhibitory activity against Escherichia coli and Staphylococcus aureus.

Cystatins may confer viral resistance in plants by inhibition of a virus-induced cell death phenomenon in which cysteine proteinases are active: cloning and molecular characterization of a cDNA encoding cysteine-proteinase inhibitor (celostatin) from Celosia cristata (crested cock's comb)

Cystatins (cysteine proteinase inhibitors) have been recently used in plants as antiviral strategy against those viruses whose replication involves cysteine proteinase activity. We proposed an idea that cystatins may confer resistance by inhibition of a virus-induced cell-death phenomenon in which cysteine proteinases are active. To test this idea, a full-length cDNA library was constructed from the preflowering stage of Celosia cristata (crested cock's comb) leaves, and a cDNA clone with cystatin domain was isolated using an oligonucleotide probe designed on the basis of the conserved peptide of plant cystatins. It was expressed in an Escherichia coli expression system as a fusion protein. The purified recombinant product, termed 'celostatin' (Celosia cystatin), inhibited the enzymatic activity of papain indicating its cystatin activity and prevented TMV (tobacco mosaic virus)-induced hypersensitive-response cell death in Nicotiana glutinosa (a wild species of tobacco) leaves by 65-70% at the concentration of approx. 50 ng/ml. It also offered resistance against TMV and caused normal growth of the test plant. Since the activity of cysteine proteinases is not involved in the TMV replication process, we speculated that inhibition of the hypersensitive response by celostatin may be due to the inactivation of proteolysis involved in the plant cell death programme, a phenomenon that has already been reported in animal systems.

The strawberry gene Cyf1 encodes a phytocystatin with antifungal properties

An EST, encoding a strawberry phytocystatin (PhyCys) obtained from a developing fruit of Fragariaxananassa cv. Elsanta has been characterized. The corresponding gene (Cyf1) had three introns interrupting its ORF that codes for a protein (FaCPI-1) of 235 amino acid residues with a putative signal peptide of 29 residues and an estimated molecular mass for the mature protein of 23.1 kDa. This protein contains, besides a C-terminal extension, several motifs conserved in all members of the PhyCys superfamily: (i) a GG and LARFAV-like motifs towards the N-terminal part of the protein; (ii) the reactive site QVVAG, and (iii) a conserved PW, downstream of the reactive site. Northern blot and in situ hybridization analyses indicated that the Cyf1 gene was expressed in fully expanded leaves, in roots and in achenes, but not in the receptacle (pseudocarp) during fruit development. The recombinant FaCPI-1 protein expressed in E. coli efficiently inhibited papain (K(i) 1.9 x 10(-9) M) and less so cathepsin H (K(i) 4.7 x 10(-7) M) and cathepsin B (K(i) 3.3 x 10(-6) M), and was a good inhibitor of the in vitro growth of phytopathogenic fungi Botrytis cinerea (EC(50): 1.90 microM) and Fusarium oxysporum (EC(50): 2.28 microM).

Maize cystatins respond to developmental cues, cold stress and drought

Comprehensive searches of maize EST data allowed us to identify 8 novel Corn Cystatin (CC) genes in addition to the previously known genes CCI and CCII. The deduced amino acid sequences of all 10 genes contain the typical cystatin family signature. In addition, they show an extended overall similarity with cystatins from other species that belong to several different phyto-cystatin subfamilies. To gain further insight into their respective roles in the maize plant, gene-specific expression profiles were established by semi-quantitative RT-PCR. While 7 CC genes were expressed in two or more tissues varying from gene to gene, CCI was preferentially expressed in immature tassels and CC8 and CC10 in developing kernels. As shown by in situ hybridisation of maize kernels, CC8 was specifically expressed in the basal region of the endosperm and CC10 both in the starchy endosperm and the scutellum of the embryo. The remaining, not kernel-specific genes, all had distinct expression kinetics during kernel development, generally with peaks during the early stages. In addition to developmental regulation, the effect of cold stress and water starvation were tested on cystatin expression. Two genes (CC8 and CC9) were induced by cold stress and 5 genes (CCII, CC3, CC4, CC5 and CC9) were down-regulated in response to water starvation. Taken together our data suggest distinct functions for CC genes in the maize plant.

Comparative phylogenetic analysis of cystatin gene families from arabidopsis, rice and barley

The plant cystatins or phytocystatins comprise a family of specific inhibitors of cysteine proteinases. Such inhibitors are thought to be involved in the regulation of several endogenous processes and in defence against pests and pathogens. Extensive searches in the complete rice and Arabidopsis genomes and in barley EST collections have allowed us to predict the presence of twelve different cystatin genes in rice, seven in Arabidopsis, and at least seven in barley. Structural comparisons based on alignments of all the protein sequences using the CLUSTALW program and searches for conserved motifs using the MEME program have revealed broad conservation of the main motifs characteristic of the plant cystatins. Phylogenetic analyses based on their deduced amino acid sequences have allowed us to identify groups of orthologous cystatins, and to establish homologies and define examples of gene duplications mainly among the rice and barley cystatin genes. Moreover, the absence of a counterpart between the two monocots, as well as strong variations in the motifs that interact with the cysteine proteinases, may be related to a species-specific evolutionary process. This cystatin classification should facilitate the assignment of proteinase specificities and functions to other cystatins as new information is obtained.

Deciphering genetic variations of proteome responses to water deficit in maize leaves

The proteome of the basal part of growing Zea mays leaves was analyzed from 4 to 14 d after stopping watering and in well watered controls. The relative quantity of 46 proteins was found to increase in leaves of plants submitted to water deficit. Different types of responses were observed, some proteins showing a constant increase during water deficit, while others showed stabilization after a first increase or a transient increase. Isoforms encoded by the same gene showed different responses. The response to water deficit showed genetic variation. Some increased proteins were induced specifically in one of the two studied genotypes (e.g. ASR1) while others were significantly induced in both genotypes but to a different level or with different kinetics. Analyses of relations between protein quantities, relative water content (RWC) and abscisic acid (ABA) concentration allowed us to show that the quantitative variation of some proteins (e.g. ABA45 and OSR40 proteins) was linked to differences in ABA accumulation between the genotypes. Other proteins showed genetic variations that were not related to differences in water status or ABA concentration (e.g. a cystatin). Data obtained from these experiments, together with data from other experiments, contribute to the characterization of maize proteome response to drought in different conditions and in different genotypes. This characterization allows the search for candidate proteins, i.e. for protein whose genetic variation of expression could be partly responsible for the variability of plant responses to drought.

Protein proteinase inhibitor genes in combat against insects, pests, and pathogens: natural and engineered phytoprotection

The continual need to increase food production necessitates the development and application of novel biotechnologies to enable the provision of improved crop varieties in a timely and cost-effective way. A milestone in this field was the introduction of Bacillus thuringiensis (Bt) entomotoxic proteins into plants. Despite the success of this technology, there is need for development of alternative strategies of phytoprotection. Biotechnology offers sustainable solutions to the problem of pests, pathogens, and plant parasitic nematodes in the form of other insecticidal protein genes. A variety of genes, besides (Bt) toxins that are now available for genetic engineering for pest resistance are genes for vegetative insecticidal proteins, proteinase inhibitors, alpha-amylase inhibitors, and plant lectins. This review presents a comprehensive summary of research efforts that focus on the potential use and advantages of using proteinase inhibitor genes to engineer insect- and pest-resistance. Crop protection by means of PI genes is an important component of Integrated Pest Management programmes.

A multicystatin is induced by drought-stress in cowpea (Vigna unguiculata(L.) Walp.) leaves

Cystatins are protein inhibitors of cystein proteinases belonging to the papain family. In cowpea, cystatin-like polypeptides and a cDNA have been identified from seeds and metabolic functions have been attributed to them. This paper describes VuC1, a new cystatin cDNA isolated from cowpea leaves (Vigna unguiculata (L.) Walp.). Sequence analysis revealed a multicystatin structure with two cystatin-like domains. The recombinant VUC1 protein (rVUC1) was expressed in an heterologous expression system and purified to apparent homogeneity. It appeared to be an efficient inhibitor of papain activity on a chromogenic substrate. Polyclonal antibodies against rVUC1 were obtained. Involvement of the VuC1 cDNA in the cellular response to various abiotic stresses (progressive drought-stress, dessication and application of exogenous abscissic acid) was studied, using Northern blot and Western blot analysis, in the leaf tissues of cowpea plants corresponding to two cultivars with different capacity to tolerate drought-stress. Surprisingly, these abiotic stresses induced accumulation of two VuC1-like messages both translated into VUC1-like polypeptides. Difference in the transcript accumulation patterns was observed between the two cultivars and related to their respective tolerance level. Presence of multiple cystatin-like polypeptides and their possible involvement in the control of leaf protein degradation by cysteine proteinases is discussed.

A Kunitz-type inhibitor of coleopteran proteases, isolated from Adenanthera pavonina L. seeds and its effect on Callosobruchus maculatus

The cowpea weevil Callosobruchus maculatus is one of the major pests of Vigna unguiculata cowpea. Digestion in the cowpea weevil is facilitated by high levels of cysteine and aspartic acid proteinases. Plants synthesize a variety of molecules, including proteinaceous proteinase inhibitors, to defend themselves against attack by insects. In this work, a trypsin inhibitor (ApTI) isolated from Adenanthera pavonina seeds showed activity against papain. The inhibition of papain by ApTI was of the noncompetitive type, with a K(i) of 1 microM. ApTI was highly effective against digestive proteinases from C. maculatus, Acanthoscelides obtectus (bean weevil), and Zabrotes subfasciatus (Mexican bean weevil) and was moderately active against midgut proteinases from the boll weevil Anthonomus grandis and the mealworm Tenebrio molitor. In C. maculates fed an artificial diet containing 0.25% and 0.5% ApTI (w/w), the latter concentration caused 50% mortality and reduced larval weight gain by approximately 40%. The action of ApTI on C. maculatus larvae may involve the inhibition of ApTI-sensitive cysteine proteinases and binding to chitin components of the peritrophic membrane (or equivalent structures) in the weevil midgut.