Circadian expression and induction by wounding of tobacco genes for cysteine proteinase

Characterization of natural leaf senescence in tobacco (Nicotiana tabacum) plants grown in vitro

Leaf senescence is a highly regulated final phase of leaf development preceding massive cell death. It results in the coordinated degradation of macromolecules and the subsequent nutrient relocation to other plant parts. Very little is still known about early stages of leaf senescence during normal leaf ontogeny that is not triggered by stress factors. This paper comprises an integrated study of natural leaf senescence in tobacco plants grown in vitro, using molecular, structural, and physiological information. We determined the time sequence of ultrastructural changes in mesophyll cells during leaf senescence, showing that the degradation of chloroplast ultrastructure fully correlated with changes in chlorophyll content. The earliest degenerative changes in chloroplast ultrastructure coinciding with early chromatin condensation were observed already in mature green leaves. A continuum of degradative changes in chloroplast ultrastructure, chromatin condensation and aggregation, along with progressive decrease in cytoplasm organization and electron density were observed in the course of mesophyll cells ageing. Although the total amounts of endogenous cytokinins gradually increased during leaf ontogenesis, the proportion of bioactive cytokinin forms, as well as their phosphate precursors, in total cytokinin content rapidly declined with ageing. Endogenous indole-3-acetic acid (IAA) levels were strongly reduced in senescent leaves, and a decreasing tendency was also observed for abscisic acid (ABA) levels. Senescence-associated tobacco cysteine proteases (CP, E.C. 3.4.22) CP1 and CP23 genes were induced in the initial phase of senescence. Genes encoding glutamate dehydrogenase (GDH, E.C. 1.4.1.2) and one isoform of cytosolic glutamine synthetase (GS1, E.C. 6.3.1.2) were induced in the late stage of senescence, while chloroplastic GS (GS2) gene showed a continuous decrease with leaf ageing.

Identification, Characterization and Down-Regulation of Cysteine Protease Genes in Tobacco for Use in Recombinant Protein Production

Plants are an attractive host system for pharmaceutical protein production. Many therapeutic proteins have been produced and scaled up in plants at a low cost compared to the conventional microbial and animal-based systems. The main technical challenge during this process is to produce sufficient levels of recombinant proteins in plants. Low yield is generally caused by proteolytic degradation during expression and downstream processing of recombinant proteins. The yield of human therapeutic interleukin (IL)-10 produced in transgenic tobacco leaves was found to be below the critical level, and may be due to degradation by tobacco proteases. Here, we identified a total of 60 putative cysteine protease genes (CysP) in tobacco. Based on their predicted expression in leaf tissue, 10 candidate CysPs (CysP1-CysP10) were selected for further characterization. The effect of CysP gene silencing on IL-10 accumulation was examined in tobacco. It was found that the recombinant protein yield in tobacco could be increased by silencing CysP6. Transient expression of CysP6 silencing construct also showed an increase in IL-10 accumulation in comparison to the control. Moreover, CysP6 localizes to the endoplasmic reticulum (ER), suggesting that ER may be the site of IL-10 degradation. Overall results suggest that CysP6 is important in determining the yield of recombinant IL-10 in tobacco leaves.

Use of transgenic oryzacystatin-I-expressing plants enhances recombinant protein production

Plants are an effective and inexpensive host for the production of commercially interesting heterologous recombinant proteins. The Escherichia coli-derived glutathione reductase was transiently expressed as a recombinant model protein in the cytosol of tobacco plants using the technique of leaf agro-infiltration. Proteolytic cysteine protease activity progressively increased over time when glutathione reductase accumulated in leaves. Application of cysteine protease promoter-GUS fusions in transgenic tobacco identified a cysteine protease NtCP2 expressed in mature leaves and being stress responsive to be expressed as a consequence of agro-infiltration. Transgenic tobacco plants constitutively expressing the rice cysteine protease inhibitor oryzacystatin-I had significantly lower cysteine protease activity when compared to non-transgenic tobacco plants. Lower cysteine protease activity in transgenic plants was directly related to higher glutathione reductase activity and also higher glutathione reductase amounts in transgenic plants. Overall, our work has demonstrated as a novel aspect that transgenic tobacco plants constitutively expressing an exogenous cysteine protease inhibitor have the potential for producing more recombinant protein which is very likely due to the reduced activity of endogenous cysteine protease.

Isolation and characterization of a gene encoding a polyethylene glycol-induced cysteine protease in common wheat

Plant cysteine protease (CP) genes are induced by abiotic stresses such as drought, yet their functions remain largely unknown. We isolated the full-length cDNA encoding a Triticum aestivum CP gene, designated TaCP, from wheat by the rapid amplification of cDNA ends (RACE) method. Sequence analysis revealed that TaCP contains an open reading frame encoding a protein of 362 amino acids, which is 96% identical to barley cysteine protease HvSF42. The TaCP transcript level in wheat seedlings was upregulated during polyethylene glycol (PEG) stress, with a peak appearing around 12 h after treatment. TaCP expression level increased rapidly with NaCl treatment at 48 h. TaCP responded strongly to low temperature (4 degree C) treatment from 1 h post-treatment and reached a peak of about 40-fold at 72 h. However, it showed only a very slight response to abscisic acid (ABA). More than one copy of TaCP was present in each of the three genomes of hexaploid wheat and its diploid donors. TaCP fused with green fluorescent protein (GFP) was located in the plasma membrane of onion epidermis cells. Transgenic Arabidopsis plants overexpressing TaCP showed stronger drought tolerance and higher CP activity under water-stressed conditions than wild-type Arabidopsis plants. The results suggest that TaCP plays a role in tolerance to water deficit.

Differential metabolic response of cultured rice (Oryza sativa) cells exposed to high- and low-temperature stress

Global mean temperatures are expected to rise by 2-4.5 degrees C by 2100, accompanied by an increase in frequency and amplitude of extreme temperature events. Greater climatic extremes and an expanded range of cultivation will expose rice to increasing stress in the future. Understanding gene expression in disparate thermal regimes is important for the engineering of cultivars with tolerance to nonoptimal temperatures. Our study investigated the proteomic responses of rice cell suspension cultures to sudden temperature changes. Cell cultures grown at 28 degrees C were subjected to 3-day exposure to 12 or 20 degrees C for low-temperature stress, and 36 or 44 degrees C for high-temperature stress. Quantitative label-free shotgun proteomic analysis was performed on biological triplicates of each treatment. Over 1900 proteins were expressed in one or more temperature treatments, and, of these, more than 850 were found to be responsive to either of the temperature extremes. These temperature-responsive proteins included more than 300 proteins which were uniquely expressed at either 12 or 44 degrees C. Our study also identified 40 novel stress-response proteins and observed that switching between the classical and the alternative pathways of sucrose metabolism occurs in response to extremes of temperature.

Understanding the physiological and molecular mechanism of persistent organic pollutant uptake and detoxification in cucurbit species (zucchini and squash)

Cucurbita pepo ssp pepo (zucchini) roots phytoextract significant amounts of persistent organic pollutants (POPs) from soil, followed by effective translocation to aboveground tissues. The closely related C. pepo ssp ovifera (squash) does not have this ability. In a DDE-contaminated field soil, zucchini roots and stems contained 3.6 and 6.6-fold greater contaminant than did squash tissues, respectively, and zucchini phytoextracted 12-times more DDE from soil than squash. In batch hydroponics, squash was significantly more sensitive to DDE (2-20 mg/L) exposure; 4 mg/L DDE significantly reduced squash biomass (14%) whereas for zucchini, biomass reductions were observed at 20 mg/L (20%). PCR select Suppression Subtraction Hybridization was used to identify differentially expressed genes in DDE treated zucchini relative to DDE treated squash or non-treated zucchini. After differential screening to eliminate false positives, unique cDNA clones were sequenced. Out of 40 shoot cDNA sequences, 34 cDNAs have homology to parts of phloem filament protein 1 (PP1). Out of 6 cDNAs from the root tissue, two cDNAs are similar to cytochrome P450 like proteins, and one cDNA matches a putative senescence associated protein. From the DDE exposed zucchini seedlings cDNA library, out of 22 differentially expressed genes, 14 cDNAs were found to have homology with genes involved in abiotic stresses, signaling, lipid metabolism, and photosynthesis. A large number of cDNA sequences were found to encode novel unknown proteins that may be involved in uncharacterized pathways of DDE metabolism in plants. A semiquantitative RT-PCR analysis of isolated genes confirmed up-regulation in response to DDE exposure.

Cloning and characterization of a novel cysteine protease gene (HbCP1) from Hevea brasiliensis

The full-length cDNA encoding a cysteine protease,designated HbCP1, was isolated for the first time from Hevea brasiliensis by the rapid amplification of cDNA ends (RACE) method. HbCP1 contained a 1371 bp open reading frame encoding 457 amino acids.The deduced HbCP1 protein,which showed high identity to cysteine proteases of other plant species,was predicted to possess a putative repeat in toxin (RTX) domain at the N-terminal and a granulin (GRAN) domain at the C-terminal.Southern blot analysis indicated that the HbCP1 gene is present as a single copy in the rubber tree.Transcription pattern analysis revealed that HbCP1 had high transcription in laticifer,and low transcription in bark and leaf.The transcription of HbCP1 in latex was induced by ethylene and tapping.Cloning of the HbCP1 gene will enable us to further understand the molecular characterization of cysteine protease and its possible function in the rubber tree.

Isolation and characterization of a cDNA encoding a papain-like cysteine protease from alfalfa

Protein hydrolyzation is activated and involved in response to various stress signals. In the present study, a full-length cDNA, named MsCP1, encoding a papain-like cysteine protease was obtained by degenerated primers and 3'- and 5'-RACE from salt-tolerant alfalfa. The cDNA contained an open reading frame encoding a deduced protein of 350 amino acids with a putative N-terminal signal peptide, NPIR vacuole-sorting signal sequence and potential N-linked glycosylation sites. The deduced sequence showed a high similarity to deduced proteins from pea, tobacco, tomato and ryegrass. Fusion expression analysis in Escherichia coli showed that the putative eukaryotic signal peptide prevented its expression in prokaryotic system. The integration and transcript of the expression elements in transgenic tobacco plants were detected with Southern blot and RT-PCR analysis.

Cysteine proteinases regulate chloroplast protein content and composition in tobacco leaves: a model for dynamic interactions with ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) vesicular bodies

The roles of cysteine proteinases (CP) in leaf protein accumulation and composition were investigated in transgenic tobacco (Nicotiana tabacum L.) plants expressing the rice cystatin, OC-1. The OC-1 protein was present in the cytosol, chloroplasts, and vacuole of the leaves of OC-1 expressing (OCE) plants. Changes in leaf protein composition and turnover caused by OC-1-dependent inhibition of CP activity were assessed in 8-week-old plants using proteomic analysis. Seven hundred and sixty-five soluble proteins were detected in the controls compared to 860 proteins in the OCE leaves. A cyclophilin, a histone, a peptidyl-prolyl cis-trans isomerase, and two ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase isoforms were markedly altered in abundance in the OCE leaves. The senescence-related decline in photosynthesis and Rubisco activity was delayed in the OCE leaves. Similarly, OCE leaves maintained higher leaf Rubisco activities and protein than controls following dark chilling. Immunogold labelling studies with specific antibodies showed that Rubisco was present in Rubisco vesicular bodies (RVB) as well as in the chloroplasts of leaves from 8-week-old control and OCE plants. Western blot analysis of plants at 14 weeks after both genotypes had flowered revealed large increases in the amount of Rubisco protein in the OCE leaves compared to controls. These results demonstrate that CPs are involved in Rubisco turnover in leaves under optimal and stress conditions and that extra-plastidic RVB bodies are present even in young source leaves. Furthermore, these data form the basis for a new model of Rubisco protein turnover involving CPs and RVBs.

Infection of tobacco with different Pseudomonas syringae pathovars leads to distinct morphotypes of programmed cell death

Tobacco plants (Nicotiana tabacum cv. Xanthi-nc) infiltrated with either of two pathovars of Pseudomonas syringae- an avirulent strain of P. syringae pv. tabaci (Pst) or the non-host pathogen P. syringae pv. maculicola M2 (Psm) - developed a hypersensitive response (HR). There were considerable differences in HR phenotype, timing and sequence of cell dismantling between the two pathosystems. Following Psm infiltration, the first macroscopic signs were visible at 4.5 h post-infiltration (hpi). Simultaneously, increased plasma membrane permeability was observed, suggesting that the loss of cell membrane integrity initiates the macroscopic HR evoked by Psm. In contrast, after Pst treatment there was a distinct time lapse between the first signs of tissue collapse (9 hpi) and the occurrence of plasma membrane discontinuity (12 hpi). Ultrastructural studies of cells undergoing the HR triggered by Psm and Pst revealed distinct patterns of alterations in morphology of organelles. Moreover, while different forms of nuclear degeneration were observed in leaf zones infiltrated with Pst, we failed to detect any abnormalities in the nuclei of Psm-treated tissue. In addition, application of synthetic caspase inhibitors (Ac-DEVD-CHO, Ac-YVAD-CMK) abolished HR induced by Pst, but not Psm. Our observations suggest that different cell death mechanisms are executed in response to Psm and Pst. Interestingly, pre-inoculation with Pst, but not with Psm, induced a long-distance acquired resistance (LDAR) response, even though locally a typical set of defense responses, including acquired resistance, was activated locally in response to Psm. The failure of Psm to induce LDAR may be due to the rapid degeneration of bundle sheath cells resulting from Psm infection.

Gliadain, a gibberellin-inducible cysteine proteinase occurring in germinating seeds of wheat, Triticum aestivum L., specifically digests gliadin and is regulated by intrinsic cystatins

We cloned a new cysteine proteinase of wheat seed origin, which hydrolyzed the storage protein gliadin almost specifically, and was named gliadain. Gliadain mRNA was expressed 1 day after the start of seed imbibition, and showed a gradual increase thereafter. Gliadain expression was suppressed when uniconazol, a gibberellin synthesis inhibitor, was added to germinating seeds. Histochemical detection with anti-gliadain serum indicated that gliadain was present in the aleurone layer and also that its expression intensity increased in sites nearer the embryo. The enzymological characteristics of gliadain were investigated using recombinant glutathione S-transferase (GST)-progliadain fusion protein produced in Escherichia coli. The GST-progliadain almost specifically digested gliadin into low molecular mass peptides. These results indicate that gliadain is produced via gibberellin-mediated gene activation in aleurone cells and secreted into the endosperm to digest its storage proteins. Enzymologically, the GST-progliadain hydrolyzed benzyloxycarbonyl-Phe-Arg-7-amino-4-methylcoumarin (Z-Phe-Arg-NH(2)-Mec) at K(m) = 9.5 microm, which is equivalent to the K(m) value for hydrolysis of this substrate by cathepsin L. Hydrolysis was inhibited by two wheat cystatins, WC1 and WC4, with IC(50) values of 1.7 x 10(-8) and 5.0 x 10(-8) m, respectively. These values are comparable with those found for GST-progliadain inhibition by E-64 and egg-white cystatin, and are consistent with the possibility that, in germinating wheat seeds, gliadain is under the control of intrinsic cystatins.

Virus-derived genes for insect-resistant transgenic plants

Insect viruses have evolved to counter physiological barriers to infection presented by the host insect. For the Lepidoptera (butterflies and moths), these barriers include (1) the peritrophic membrane (PM) lining the gut, which presents a physical barrier to virus infection of the midgut epithelial cells, (2) the basement membrane (BM) that overlies the gut thereby restricting secondary infection of other tissues, and (3) the immune system of the host insect. Hence, insect viruses provide a resource for genes that disrupt host physiology in a specific manner, and these genes in turn serve as a resource both for the study of physiological processes, and for disruption of these processes for pest management purposes. There are several examples of the application of genes used by an insect virus to overcome the PM barrier for production of insect-resistant transgenic plants. There are other examples of intrahemocoelic effectors, such as BM-degrading proteases that can only be used with an appropriate system for delivery of the agent from the gut into the hemocoel (body cavity) of the insect pest. In this chapter, we describe (1) baculovirus- and entomopoxvirus-derived genes that alter the physiology of the host insect, (2) use of these and homologous genes for production of insect-resistant transgenic plants, (3) other viral genes that have potential for use in development of insect-resistant transgenic plants, and (4) the use of plant lectins for delivery of intrahemocoelic toxins from transgenic plants. Plant expression of polydnavirus-derived genes is described by Gill et al. (this volume, pp. 393-426).

Effects of mechanical wounding on Carica papaya cysteine endopeptidases accumulation and activity

The mechanical wounding impact on the Carica papaya latex protein pattern was investigated by analyzing three latexes. A first one commercially available, a second harvested from unripe but fully grown fruits, both obtained from regularly tapped fruits. A third one was collected from similar fruits but wounded for the first time. The results demonstrated both quantitative and qualitative changes in the protein content and in the enzymatic activity. Repeated wounding results in either, accumulation or activation (or both of them) of papain, chymopapain and caricain. Furthermore, new cysteine protease activity was found to transiently accumulate in the latex collected from newly wounded fruits. The possible implication of this enzymatic material in the papaya cysteine endopeptidases pro-forms activation is discussed.

Two new cysteine proteinases with specific expression patterns in mature and senescent tobacco (Nicotiana tabacum L.) leaves

Cysteine proteinases are involved in various physiological and developmental processes in plants. Two cDNAs from senescent and non-senescent tobacco leaves were isolated with degenerate primers designed from conserved regions of plant senescence-associated cysteine proteinases using rapid amplification of cDNA ends (RACE). Both sequences encode papain-like cysteine proteinases: the 833 bp fragment (NtCP1) encoding a C-terminus partial sequence of a putative tobacco cysteine proteinase gene whereas the 1300 bp fragment (NtCP2) is a full-length cysteine proteinase. On the amino acid sequence level, NtCP1 has a high similarity with other senescence-associated cysteine proteinases. It is expressed only in senescent leaves. It is not induced in mature green leaves upon exposure to drought or heat. These results suggest that it might be a good developmental senescence marker in tobacco. By contrast, NtCP2 has a high similarity to KDEL-tailed cysteine proteinases and is expressed in mature green leaves. Both drought and heat decreased NtCP2 transcript abundance in mature green leaves. It is concluded that NtCP1 is a senescence-specific cysteine proteinase whereas NtCP2 fulfils roles in green leaves that might be similar to those of KDEL-tailed cysteine proteinases involved, for example, in programmed cell death.

Ethylene-sensitivity regulates proteolytic activity and cysteine protease gene expression in petunia corollas

To investigate ethylene's role in petal senescence, a comparative analysis of age-related changes in total protein, protease activity, and the expression of nine cysteine protease genes in the corollas of ethylene-sensitive Petuniaxhybrida cv. Mitchell Diploid (MD) and ethylene-insensitive (35S:etr1-1; line 44568) transgenic petunias was conducted. The later stages of corolla senescence in MD flowers were associated with decreased fresh weight, decreased total protein, and increased proteolytic activity. Corolla senescence was delayed by approximately 8 d in etr-44568 transgenic petunias, and decreases in corolla fresh weight, protein content, and maximum proteolytic activity were similarly delayed. Protease inhibitor studies indicated that the majority of the protease activity in senescing petals was due to cysteine proteases. Nine cysteine proteases expressed in petals were subsequently identified. Northern blot analysis indicated that six of the nine cysteine proteases showed increased transcript abundance during petal senescence. One of these cysteine proteases, PhCP10, was detected only in senescing tissues. Expression of four of the senescence-associated cysteine proteases was delayed, but not prevented in etr-44568 flowers. The other two senescence associated cysteine proteases had high levels of transcript accumulation in etr-44568 corollas at 8 d after flower opening, when MD flowers were senescing. These patterns suggest that age-related factors, other than ethylene, were regulating the up-regulation of these genes during flower ageing. The delay in visible symptoms and biochemical and molecular indicators of senescence in ethylene-insensitive flowers is consistent with the concept that ethylene modulates the timing of senescence pathways in petals.

Identification of cis-elements for ethylene and circadian regulation of the Solanum melongena gene encoding cysteine proteinase

We have previously shown that the expression of SmCP which encodes Solanum melongena cysteine proteinase is ethylene-inducible and is under circadian control. To understand the regulation of SmCP, a 1.34-kb SmCP 5'-flanking region and its deletion derivatives were analyzed for cis-elements using GUS and luc fusions and by in vitro binding assays. Analysis of transgenic tobacco transformed with SmCP promoter-GUS constructs confirmed that the promoter region -415/+54 containing Ethylene Responsive Element ERE(-355/-348) conferred threefold ethylene-induction of GUS expression, while -827/+54 which also contains ERE(-683/-676), produced fivefold induction. Using gel mobility shift assays, we demonstrated that each ERE binds nuclear proteins from both ethephon-treated and untreated 5-week-old seedlings, suggesting that different transcriptions factors bind each ERE under varying physiological conditions. Binding was also observed in extracts from senescent, but not young, fruits. The variation in binding at the EREs in fruits and seedlings imply that organ-specific factors may participate in binding. Analysis of transgenic tobacco expressing various SmCP promoter-luc constructs containing wild-type or mutant Evening Elements (EEs) confirmed that both conserved EEs at -795/-787 and -785/-777 are important in circadian control. We confirmed the binding of total nuclear proteins to EEs in gel mobility shift assays and in DNase I footprinting. Our results suggest that multiple proteins bind the EEs which are conserved in plants other than Arabidopsis and that functional EEs and EREs are present in the 5'-flanking region of a gene encoding cysteine proteinase.

Spider dragline silk proteins in transgenic tobacco leaves: accumulation and field production

Spider dragline silk is a unique biomaterial and represents nature's strongest known fibre. As it is almost as strong as many commercial synthetic fibres, it is suitable for use in many industrial and medical applications. The prerequisite for such a widespread use is the cost-effective production in sufficient quantities for commercial fibre manufacturing. Agricultural biotechnology and the production of recombinant dragline silk proteins in transgenic plants offer the potential for low-cost, large-scale production. The purpose of this work was to examine the feasibility of producing the two protein components of dragline silk (MaSp1 and MaSp2) from Nephila clavipes in transgenic tobacco. Two different promoters, the enhanced CaMV 35S promoter (Kay et al., 1987) and a new tobacco cryptic constitutive promoter, tCUP (Foster et al., 1999) were used, in conjunction with a plant secretory signal (PR1b), a translational enhancer (alfalfa mosaic virus, AMV) and an endoplasmic reticulum (ER) retention signal (KDEL), to express the MaSp1 and MaSp2 genes in the leaves of transgenic plants. Both genes expressed successfully and recombinant protein accumulated in transgenic plants grown in both greenhouse and field trials.

Characterization of a proteinase inhibitor from Brachypodium distachyon suggests the conservation of defence signalling pathways between dicotyledonous plants and grasses

SUMMARY Proteinase inhibitors (PIs) are established markers for wound- and especially jasmonate-mediated signalling in dicot species such as tomato and potato. Differential screening of a cDNA library constructed from RNA isolated from wounded leaves of the grass Brachypodium distachyon led to the identification of a proteinase inhibitor gene (Bdpin1). Bdpin1 exhibited the highest homology to the subtilisin/chymotrypsin-inhibiting subgroup of the pin1 class of plant PIs. Northern analyses indicated that Bdpin1 was induced within 6 h at the site of wounding and systemically, by 24 h, thereby providing evidence for long-distance signalling in grasses. Bdpin1 also proved to be more rapidly induced in susceptible than in resistant ecotypes of B. distachyon following challenge with the Rice blast pathogen, Magnaporthe grisea. Screening with chemical signals indicated that Bdpin1 could be induced with MeJA but not with the putative mimic of salicylic acid, benzothiadiazole. Genomic Southern hybridization was consistent with Bdpin1 existing at a single locus, which was isolated following screening of a genomic cosmid library. DNA upstream of the Bdpin1 coding sequence was characterized via fusion to a GUS reporter and was found to confer wound-responsive transcription in B. distachyon and other cereals following biolistic bombardment. Both wound- and TMV-activated Bdpin1-GUS activity was detected in transgenic tobacco. Given that B. distachyon represents an ancestral grass species, our data suggest that there is considerable conservation in defence-associated signalling between dicots and grasses.

Identification of dehydration-responsive cysteine proteases during post-harvest senescence of broccoli florets

Harvest-induced senescence of broccoli results in tissue wilting and sepal chlorosis. As senescence progresses, chlorophyll and protein levels in floret tissues decline and endo-protease activity (measured with azo-casein) increases. Protease activity increased from 24 h after harvest for tissues held in air at 20 degrees C. Activity was lower in floret tissues from branchlets that had been held in solutions of sucrose (2% w/v) or under high carbon dioxide, low oxygen (10% CO(2), 5% O(2)) conditions. Four protease-active protein bands were identified in senescing floret tissue by zymography, and the use of chemical inhibitors of protease action suggests that some 44% of protease activity in senescing floret tissue 72 h after harvest is due to the action of cysteine and serine proteases. Four putative cysteine protease cDNAs have been isolated from broccoli floret tissue (BoCP1, BoCP2, BoCP3, BoCP4). The cDNAs are most similar (73-89% at the amino acid level) to dehydration-responsive cysteine proteases previously isolated from Arabidopsis thaliana (RD19, RD21). The mRNAs encoded by the broccoli cDNAs are expressed in floret tissue during harvest-induced senescence with mRNA accumulating within 6 h of harvest for BoCP1, 12 h of harvest for BoCP4 and within 24 h of harvest for BoCP2 and BoCP3. Induction of the cDNAs is differentially delayed when broccoli branchlets are held in solutions of water or sucrose. In addition, the expression of BoCP1 and BoCP3 is inhibited in tissue held in atmospheres of high carbon dioxide/low oxygen (10% CO(2), 5% O(2)). The putative cysteine protease mRNAs are expressed before measurable increases in endo-protease activity, loss of protein, chlorophyll or tissue chlorosis.

A cathepsin B-like cysteine protease gene from Hordeum vulgare (gene CatB) induced by GA in aleurone cells is under circadian control in leaves

A barley cDNA clone encoding a putative cysteine protease with sequence homology to cathepsin B from mammalian cells has been characterized. This barley gene (CatB) is ubiquitously expressed, its mRNA being detected in leaves and roots, immature, mature and germinating embryos, in developing endosperms, and in aleurones upon germination, as assessed by northern blot analysis. The CatB mRNA expression in leaves increased by cold shock (6 degrees C), was not affected by wounding, and was under circadian control. These transcripts increased in the aleurone upon germination, whereas those for a cystatin encoding gene (Icy), that inhibits commercial cathepsin B in vitro, decreased. Gibberellin (GA) treatment of isolated barley aleurones induced and abscisic acid (ABA) repressed the steady-state levels of CatB mRNA, while Icy expression had an opposite pattern of mRNA accumulation in aleurones treated with GA. No response to GA or ABA was detected in leaves.

Oryzacystatin I expression in transformed tobacco produces a conditional growth phenotype and enhances chilling tolerance

A recent strategy for pest control in plants has involved transformation with genes encoding cysteine proteinase inhibitors (cystatins). Little is known, however, about the effects of constitutive cystatin expression on whole plant physiology. The present study using oryzacystatin I (OC-I) expression in transformed tobacco was designed to resolve this issue and also to test the effects on abiotic stress tolerance. All transformed plants expressing OC-I showed a conditional phenotype. A marked effect on stem elongation was observed in plants grown under low light intensities. After 7 weeks of growth at low light, the plants expressing OC-I were smaller with fewer expanded leaves and a slightly lower total biomass than empty vector controls or wild type plants. Maximal rates of photosynthesis (A(max)) were also decreased, the inhibitory effect being greatest in the plants with highest OC-I expression. After 12 weeks of growth at low light, however, the plants expressing OC-I performed better in terms of shoot biomass production, which was nearly double that of the empty vector or wild type controls. All plants showed similar responses to drought, however photosynthesis was better protected against chilling injury in plants constitutively expressing OC-I. Photosynthetic CO(2) assimilation was decreased in all plants following exposure to 5 degrees C, but the inhibition was significantly less in the OC-I expressing plants than in controls. The transformed tobacco plants expressing OC-I therefore show a phenotype-environment interaction with important implications for biotechnological applications.

Hieronymain I, a new cysteine peptidase isolated from unripe fruits of Bromelia hieronymi Mez (Bromeliaceae)

A new peptidase, named hieronymain I, was purified to homogeneity from unripe fruits of Bromelia hieronymi Mez (Bromeliaceae) by acetone fractionation followed by cation exchange chromatography (FPLC) on CM-Sepharose FF. Homogeneity of the enzyme was confirmed by mass spectroscopy (MALDI-TOF), isoelectric focusing, and SDS-PAGE. Hieronymain is a basic peptidase (pI > 9.3) and its molecular mass was 24,066 Da. Maximum proteolytic activity on casein (>90% of maximum activity) was achieved at pH 8.5-9.5. The enzyme was completely inhibited by E-64 and iodoacetic acid and activated by the addition of cysteine; these results strongly suggest that the isolated protease should be included within the cysteine group. The N-terminal sequence of hieronymain (ALPESIDWRAKGAVTEVKRQDG) was compared with 25 plant cysteine proteases that showed more than 50% of identity.

Effect of yeast CTA1 gene expression on response of tobacco plants to tobacco mosaic virus infection

The response of tobacco (Nicotiana tabacum L. cv Xanthi-nc) plants with elevated catalase activity was studied after infection by tobacco mosaic virus (TMV). These plants contain the yeast (Saccharomyces cerevisiae) peroxisomal catalase gene CTA1 under the control of the cauliflower mosaic virus 35S promoter. The transgenic lines exhibited 2- to 4-fold higher total in vitro catalase activity than untransformed control plants under normal growth conditions. Cellular localization of the CTA1 protein was established using immunocytochemical analysis. Gold particles were detected mainly inside peroxisomes, whereas no significant labeling was detected in other cellular compartments or in the intercellular space. The physiological state of the transgenic plants was evaluated in respect to growth rate, general appearance, carbohydrate content, and dry weight. No significant differences were recorded in comparison with non-transgenic tobacco plants. The 3,3'-diaminobenzidine-stain method was applied to visualize hydrogen peroxide (H(2)O(2)) in the TMV infected tissue. Presence of H(2)O(2) could be detected around necrotic lesions caused by TMV infection in non-transgenic plants but to a much lesser extent in the CTA1 transgenic plants. In addition, the size of necrotic lesions was significantly bigger in the infected leaves of the transgenic plants. Changes in the distribution of H(2)O(2) and in lesion formation were not reflected by changes in salicylic acid production. In contrast to the local response, the systemic response in upper noninoculated leaves of both CTA1 transgenic and control plants was similar. This suggests that increased cellular catalase activity influences local but not systemic response to TMV infection.

Fluorescent differential display identifies circadian clock-regulated genes in Arabidopsis thaliana

Circadian rhythms in gene expression were first observed in plants more than 13 years ago, but the underlying mechanism controlling rhythmic gene expression is still not understood. The isolation of novel circadian clock-controlled genes (ccgs) is likely to provide new tools for studying circadian rhythms. Fluorescent differential display (FDD) was used to screen Arabidopsis thaliana mRNAs for cycling transcripts. Seventy PCR primer pairs were screened, and 17 different cycling bands were observed out of an estimated 10,500 bands screened. The identities of 10 bands were determined, and the rhythmic gene expression was confirmed using northern blot analysis. The 10 cycling bands represent 7 different genes, 6 of which are present in the databases and 1 that does not match anything in current databases. The rhythmic expression of the 7 genes is composed of four distinct phases of clock regulation. The results demonstrate that FDD can be used to isolate ccgs. The genes identified in this screen range from known A. thaliana ccgs, as well as genes shown to be clock controlled in other plant species, to a novel gene that may encode a pioneer protein. Further study of these ccgs is likely to increase our understanding of circadian-regulated gene expression.

Immunolocalization of a cysteine protease in vacuoles, vesicles, and symbiosomes of pea nodule cells

PsCYP15A is a cysteine protease from pea (Pisum sativum L.). It was first recognized as an up-regulated transcript in wilted shoots and subsequently in root nodules containing Rhizobium. Proteolytic activity of PsCYP15A in nodule extracts is now reported following immunopurification with polyclonal antiserum raised against recombinant antigen. Western-blot analysis indicated two forms of PsCYP15A, a pro-form (approximately 38 kD) and a mature form (approximately 30 kD). Both forms were present in most tissue samples, but only the mature form was isolated from cell-fractionated symbiosomes containing nitrogen-fixing bacteroids. Immunolabeling of nodule sections showed localization of PsCYP15A antigen in large vacuolar bodies, cytoplasmic vesicles, and the perisymbiont space. Immunolabeling of tissue sections from wilted shoots also indicated the presence of PsCYP15A in vacuoles and cytoplasmic vesicles. This protease may be involved in the adaptation to changes in cell turgor, both in wilted shoots and in nodule tissue. Additionally, the protease may be involved in protein turnover in the symbiosome compartment.

Purification and characterization of macrodontain I, a cysteine peptidase from unripe fruits of Pseudananas macrodontes (Morr.) harms (Bromeliaceae)

A new papain-like cysteine peptidase isolated from fruits of Pseudananas macrodontes (Morr.) Harms, a species closely related to pineapple (Ananas comosus L.), has been purified and characterized. The enzyme, named macrodontain I, is the main proteolytic component present in fruit extracts and was purified by acetone fractionation followed by anion-exchange chromatography. Separation was improved by selecting both an adequate pH value and a narrow saline gradient. Optimum pH range (more than 90% of maximum activity with casein) was achieved at pH 6.1-8.5. Homogeneity of the enzyme was confirmed by bidimensional electrophoresis and mass spectroscopy (MS). Molecular mass of the enzyme was 23,459 (MS) and its isoelectric point was 6.1. The alanine, glutamine, and tyrosine derivatives were strongly preferred when the enzyme was assayed on N-alpha-CBZ-l-amino acid p-nitrophenyl esters. The N-terminal sequence of macrodontain (by comparison with the N-terminus of 30 plant proteases with more than 50% homology) showed a great deal of sequence similarity to the other pineapple-stem-derived cysteine endopeptidases, being 85.7, 85. 2, and 77.8% identical to comosain, stem bromelain, and ananain, respectively. It seems clear that the Bromeliaceae endopeptidases are more closely related to each other than to other members of the papain family, suggesting relatively recent divergence.

Expression of cysteine proteinase during developmental events associated with programmed cell death in brinjal

Here we show that the expression of a cysteine proteinase coincides with several developmental events associated with programmed cell death (PCD) in Solanum melongena (brinjal), i.e. during leaf senescence, fruit senescence, xylogenesis, nucellar cell degeneration and anther senescence. We have isolated a cDNA encoding brinjal cysteine proteinase (SmCP) that shares high (90-92%) amino acid identity to cysteine proteinases of tobacco (CYP-8) and tomato (LCYP-2) that have not been previously reported to be senescence-associated. In contrast, SmCP shows lower (39-41%) amino acid identity to other senescence-related cysteine proteinases and, unlike most of them, it is not preferentially expressed in certain organs or cell types. Northern analysis of leaves, fruits and flowers at different stages of development showed that SmCP expression increased significantly at senescence in leaf and fruit, but was highly expressed throughout flower development. In situ hybridization studies on flower sections using an antisense RNA probe localized the SmCP mRNA to the xylem, the epidermis and the endothecium of the anther and the nucellar cells, suggesting its involvement in PCD during xylogenesis, anther senescence and ovule development, respectively. Its expression during nucellar cell degeneration suggests that protein reserves of the nucellus are released to the developing embryo. Polarity in its pattern of expression in the nucellus of the developing seed (40DAP) further implies a directional flow of these nutrients.

Significance of circadian gene expression in higher plants

The significance of the circadian clock for living organisms is not fully understood. Recent findings demonstrate circadian control of transcription of quite a number of genes with individual maxima throughout the entire day. Evidence in favor of circadian-clock-controlled translation has also been documented. In this article, we want to promote the idea that in plants the clock functions as a regulator which coordinates critical cellular processes, such as cell division, nitrate reduction, or synthesis of chlorophyll-protein complexes, in such a way that the generation of dangerous, oxidative radicals or exposure to harmful light is minimized. This has been achieved by plant organisms either by confining gene expression to the dark phase or by a tight coordination of different tiers of gene expression during the light phase. This leads to the consequence for the researcher that the time of experimentation needs to be carefully considered and documented. It also follows that one might lose important findings if only a particular portion of the day is investigated.

Molecular cloning of a tomato leaf cDNA encoding an aspartic protease, a systemic wound response protein

A full-length cDNA encoding an aspartic protease (LeAspP) has been cloned from a tomato leaf cDNA library. Using LeAspP cDNA as a probe in gel blots, LeAspP mRNA was shown to be systemically induced in tomato leaves by wounding. Application of methyl jasmonate to leaves of intact tomato plants, or supplying systemin to young tomato plants through their cut stems, induces synthesis of LeAspP mRNA. LeAspP message is regulated in tomato similar to several systemic wound response proteins (swrps) that are part of the defense response in tomato plants directed against herbivore attacks.

Induction of cysteine and serine proteases during xylogenesis in Zinnia elegans

The terminal process of xylogenesis, autolysis, is essential for the formulation of a tubular system for conduction of water and solutes throughout the whole plant. Several hydrolase types are implicated in autolysis responsible for the breakdown of cytoplasm. Here, we characterize p48h-17 cDNA from in vitro tracheary elements (TEs) of Zinnia elegans which encodes a preproprotein similar to papain. The putative mature protein, a cysteine protease, has a molecular mass of 22,699 Da with a pI of 5.7. DNA gel blot analysis indicated that p48h-17 is likely encoded by one or two genes. The p48h-17 mRNA accumulated markedly in in vitro differentiating TEs, whereas it appeared not to be induced in response to senescence and wounding in the leaves or H2O2 challenge in the cultured mesophyll cells. In stems, the expression of the p48h-17 gene was preferentially associated with differentiating xylem. Activity gel assays demonstrated that a cysteine and a serine protease, which had apparent molecular masses of 20 kDa and 60 kDa, respectively, were markedly induced during in vitro TE differentiation. The cysteine protease activity was also preferentially present in the xylem of Zinnia stems. Transient expression of the p48h-17 cDNA in tobacco protoplasts resulted in the production of a 20 kDa cysteine protease. Taken together, the results indicate that the p48h-17 gene appears to be preferentially associated with xylogenesis, and both the cysteine and serine proteases might be involved in autolysis during xylogenesis.

Isolation and expression pattern of a cDNA encoding a cathepsin B-like protease from Nicotiana rustica

Sequence analysis of a 1.33 kb clone from a root cDNA library of Nicotiana rustica revealed an open reading frame encoding a protein of 356 amino acids. The deduced protein has high levels of homology to human cathepsin B protease and a cathepsin B-like cysteine protease from wheat but much lower levels of homology with other plant cysteine proteinases. Southern blotting experiments suggest a limited number of cathepsin B-like genes are present in the genome of N. rustica and also that of N. tabacum. RNA analysis involving a range of tissues, harvested from both Nicotiana species 4-5 h after the beginning of a 16 h photoperiod, revealed the cathepsin B-like gene was being expressed strongly in roots, stem and developing flowers but weakly in mature leaves. Further analysis of RNA extracted from leaf tissue of N. tabacum revealed the gene showed rhythmic expression and also that its expression increased in response to wounding. Analysis of leaf tissues harvested during the latter part of a 16 h photoperiod (11 and 16 h after illumination commenced) showed that transcript levels were two three times higher than in leaf tissue harvested either towards the end of the dark period or 5 h after illumination commenced. When leaf tissue was wounded at 11:00 (5 h after plants were illuminated), and harvested for RNA extraction 6 h later, the level of cathepsin B-like transcript in mesophyll tissue was found to be increased ca. 2-fold relative to the level detected in unwounded controls.

A salt- and dehydration-inducible pea gene, Cyp15a, encodes a cell-wall protein with sequence similarity to cysteine proteases

The pea (Pisum sativum) gene Cyp15a encodes a protein with sequence similarity to cysteine proteases. Expression of Cyp15a was investigated during pea seedling development and in response to environmental stress. Cyp15a shows increased transcription and elevated mRNA levels in plant tissues that are partially dehydrated or treated with 0.6 M mannitol. Cyp15a mRNA levels also increase in seedlings treated with 0.2-0.25 M NaCl or KCl. During development, Cyp15a mRNA levels increase within 6 to 12 h in cotyledons and axes during germination and continue to increase for at least 96 h. Illumination of dark-grown seedlings increased Cyp15a mRNA abundance in elongating and non-elongating stem tissues. GA and ABA, which modulate the abundance of many seed-localized cysteine proteases, did not significantly modulate Cyp15a mRNA levels in stems. The protein encoded by Cyp15a contains a typical amino-terminal secretory targeting domain. This domain is followed by a pro-sequence containing ca. 110 amino acids that is found in other cysteine proteases. Polyclonal antibodies, directed against CYP15a, recognized both the larger pro-form and the cleaved mature form of CYP15a on western blots. Immunolocalization assays indicated that both forms of the protein are located in cell walls of stem cortical cells.

Dark induction and subcellular localization of the pathogenesis-related PRB-1b protein

The PRB-1b gene codes for a basic-type pathogenesis-related protein of the PR-1 family of tobacco. PRB-1b mRNA accumulation is induced in response to biotic and abiotic elicitors, such as TMV, ethylene, salicylic acid, alpha-amino butyric acid and darkness. In order to determine the location of elements that control dark-regulated PRB-1b gene expression, we tested promoter, transcribed regions and 3'-downstream regions of the gene for their ability to respond to dark induction in transgenic tobacco plants. An ethylene-inducible promoter region of 863 bp was not able to confer dark induction to a beta-glucuronidase reporter gene, while a construct containing the transcribed region of the gene and 3'-downstream sequences, driven by the cauliflower mosaic virus 35S promoter, was correctly dark-regulated. The results indicate that dark-induction of the PRB-1b gene can be controlled by 3'-downstream elements at the transcriptional level or by transcribed sequences at the post-transcriptional level. A circadian clock regulation of the PRB-1b gene was excluded, as fluctuations of PRB-1b transcript levels were not observed in plants placed in constant light or darkness. Subcellular localization of the PRB-1b protein was also determined, in tobacco protoplasts preparations and in cell cultures. The PRB-1b polypeptide was predominantly detected in protoplast vacuoles and was not secreted to the media in cell cultures. These results support an intracellular localization for the PRB-1b protein, as reported for other basic-type components of the pathogenesis-related proteins family.

Ethylene-regulated expression of a carnation cysteine proteinase during flower petal senescence

The senescence of carnation (Dianthus caryophyllus L.) flower petals is regulated by the phytohormone ethylene and is associated with considerable catabolic activity including the loss of protein. In this paper we present the molecular cloning of a cysteine proteinase and show that its expression is regulated by ethylene and associated with petal senescence. A 1600 bp cDNA was amplified by polymerase chain reaction using a 5'-specific primer and 3'-nonspecific primer designed to amplify a 1-aminocyclopropane-1-carboxylate synthase cDNA from reverse-transcribed stylar RNA. The nucleotide sequence of the cloned product (pDCCP1) was found to share significant homology to several cysteine proteinases rather than ACC synthase. A single open reading frame of 428 amino acids was shown to share significant homology with other plant cysteine proteinases including greater than 70% identity with a cysteine proteinase from Arabidopsis thaliana. Amino acids in the active site of cysteine proteinases were conserved in the pDCCP1 peptide. RNA gel blot analysis revealed that the expression of pDCCP1 increased substantially with the onset of ethylene production and senescence of petals. Increased pDCCP1 expression was also associated with ethylene production in other senescing floral organs including ovaries and styles. The pDCCP1 transcript accumulated in petals treated with exogenous ethylene within 3 h and treatment of flowers with 2,5-norbornadiene, an inhibitor of ethylene action, prevented the increase in pDCCP1 expression in petals. The temporal and spatial patterns of pDCCP1 expression suggests a role for cysteine proteinase in the loss of protein during floral senescence.

Molecular cloning and characterization of six cDNAs expressed during glucose starvation in excised maize (Zea mays L.) root tips

In order to isolate glucose-starvation-related cDNAs in maize (Zea mays L.) root tips, a cDNA library was constructed with poly(A)+ mRNA from 24 h starved root tips. After differential screening of the library, we isolated six different cDNAs (named pZSS2 and pZSS7) which were expressed during glucose starvation. Time course analysis revealed that maximum expression of five of these genes occurs 30 h after the onset of the starvation treatment. On the contrary, the expression of mRNAs corresponding to pZSS4 was maximal at an early stage of starvation and then dramatically decreased. The expression of this gene did not seem to be specific for glucose starvation. The pattern of induction of the genes corresponding to pZSS2, pZSS3, pZSS5, pZSS6 and pZSS7 revealed that non-metabolizable sugars such as L-glucose and mannitol induce mRNA transcription similarly to glucose starvation. When D-glucose or any other metabolizable sugar was supplied, the level of transcripts was reduced. Nucleotide sequence analyses of the six cDNAs allowed identification of five of them by comparison with sequence data bases. The protein encoded by clone pZSS2 is analogous to a wound-induced protein from barley. Clones pZSS4 to pZSS7 encode, respectively, a transmembrane protein, a cysteine protease, a metallothionein-like protein and a chymotrypsin/subtilisin-like protease inhibitor. Clone pZSS3 shares no significant homology with any known sequence.

cDNA cloning for a putative cysteine proteinase from developing seeds of soybean

cDNA clones for a putative cysteine proteinase were isolated from developing cotyledons of soybean (Glycine max.) using PCR-based techniques. The full-length clone of 1441 bp encodes a proteinase pre-propolypeptide of 380 amino acids. It belongs to the commonly known papain family and shows the highest sequence homology (up to 53% identity) to the protein 15A, a turgor-responsive cysteine proteinase of pea, as well as to several other stress inducible proteinases. Biosynthesis of the corresponding transcripts was shown to be developmentally controlled during embryogenesis. Southern analyses revealed occurrence of one to two genes in the soybean genome.

Characterization of a cDNA from Arabidopsis thaliana encoding a potential thiol protease whose expression is induced independently by wilting and abscisic acid

The sequence and expression characteristics are described of a wilt-inducible gene in Arabidopsis thaliana. A1494 encodes a potential thiol protease whose mRNA accumulates rapidly in shoot tissue upon the loss of turgor. A1494 mRNA levels peaked after ca. 4 h and declined thereafter. Dehydration also induced rapid biosynthesis of the phytohormone abscisic acid (ABA), which continued for at least 9 h. Exogenous ABA induced the accumulation of A1494 mRNA, with kinetics similar to those after wilting. Rehydration of wilted shoots led to a rapid decline in the content of both ABA and A1494 mRNA. Wilting and ABA independently induced A1494 expression as evidenced by the effects of ABA and wilting on the ABA-deficient aba-1 and ABA-insensitive abi-1 and abi-3 genotypes. A1494 mRNA was not detectable in aba-1 shoots but accumulated rapidly after either wilting or ABA treatment, whereas the shoot ABA content was increased only by ABA treatment. ABA had no effect on A1494 mRNA levels in the abi-1 and abi-3 mutants but wilting did result in enhanced A1494 expression. Heat shock had only a minor effect on A1494 mRNA levels, whereas exposure to low temperature resulted in substantial accumulation of A1494 mRNA in wild-type shoots. However, this latter response, unlike that to drought, was mediated exclusively via ABA synthesis as demonstrated by the lack of A1494 mRNA accumulation in cold-treated aba-1 shoots.

Tobacco proteinase inhibitor I genes are locally, but not systemically induced by stress

A cDNA library of tobacco mosaic virus (TMV)-infected tobacco was screened with polymerase chain reaction products obtained using a degenerate primer corresponding to proteinase inhibitor I (PI-I) of tomato and potato. The resulting clones encoded two highly similar, putative tobacco PI-I proteins, indicating that both genes identified in tobacco are probably expressed. The tobacco PI-I's were approximately 50% identical to wound-inducible potato and tomato PI-I and 80% identical to an ethylene-regulated tomato PI-I. Northern blot analyses indicated that healthy tobacco leaf contains only minor amounts of PI-I mRNA, and that the inhibitor genes are induced by TMV infection, salicylate treatment, ethephon spraying, UV light irradiation and wounding. The results indicate that the tobacco PI-I genes are coordinately expressed with the genes for the basic pathogenesis-related proteins. Contrary to PI-I genes of tomato and potato, wound induction of the tobacco genes occurs only locally; the upper, unwounded leaves do not show any wound-induced PI-I gene expression.