Isolation and characterization of a gene encoding a drought-induced cysteine protease in tomato (Lycopersicon esculentum)

Biotechnological Interventions in Tomato (Solanum lycopersicum) for Drought Stress Tolerance: Achievements and Future Prospects

Tomato production is severely affected by abiotic stresses (drought, flood, heat, and salt) and causes approximately 70% loss in yield depending on severity and duration of the stress. Drought is the most destructive abiotic stress and tomato is very sensitive to the drought stress, as cultivated tomato lack novel gene(s) for drought stress tolerance. Only 20% of agricultural land worldwide is irrigated, and only 14.51% of that is well-irrigated, while the rest is rain fed. This scenario makes drought very frequent, which restricts the genetically predetermined yield. Primarily, drought disturbs tomato plant physiology by altering plant–water relation and reactive oxygen species (ROS) generation. Many wild tomato species have drought tolerance gene(s); however, their exploitation is very difficult because of high genetic distance and pre- and post-transcriptional barriers for embryo development. To overcome these issues, biotechnological methods, including transgenic technology and CRISPR-Cas, are used to enhance drought tolerance in tomato. Transgenic technology permitted the exploitation of non-host gene/s. On the other hand, CRISPR-Cas9 technology facilitated the editing of host tomato gene(s) for drought stress tolerance. The present review provides updated information on biotechnological intervention in tomato for drought stress management and sustainable agriculture.

The front line of defence: a meta-analysis of apoplastic proteases in plant immunity

Secreted proteases act at the front line of defence and play pivotal roles in disease resistance. However, the criteria for apoplastic immune proteases are not always defined and followed. Here, we critically reviewed 46 apoplastic proteases that function in plant defence. We found that most apoplastic immune proteases are induced upon infection, and 17 proteases are genetically required for the immune response. Proteolytic activity has been confirmed for most of the proteases but is rarely shown to be required for biological function, and the apoplastic location of proteases can be subjective and dynamic. Pathogen-derived inhibitors have only been described for cysteine and serine proteases, and the selection pressure acting on immune proteases is rarely investigated. We discuss six different mechanisms by which these proteases mediate plant immunity and summarize the challenges for future research.

Increased water use efficiency in miR396-downregulated tomato plants

MicroRNAs regulate plant development and responses to biotic and abiotic stresses but their impact on water use efficiency (WUE) is poorly known. Increasing WUE is a major task in crop improvement programs aimed to meet the challenges posed by the reduction in water availability associated with the ongoing climatic change. We have examined the physiological and molecular response to water stress of tomato (Solanum lycopersicum L.) plants downregulated for miR396 by target mimicry. In water stress conditions, miR396-downregulated plants displayed reduced transpiration and a less then proportional decrease in the photosynthetic rate that resulted in higher WUE. The increase in WUE was associated with faster foliar accumulation of abscisic acid (ABA), with the induction of several drought-protective genes and with the activation of the jasmonic acid (JA) and γ-aminobutyric acid (GABA) pathways. We propose a model in which the downregulation of miR396 leads to the activation of a complex molecular response to water stress. This response acts synergistically with a set of leaf morphological modifications to increase stomatal closure and preserve the efficiency of the photosynthetic activity, ultimately resulting in higher WUE.

Devastating intimacy: the cell biology of plant-Phytophthora interactions

An understanding of the cell biology underlying the burgeoning molecular genetic and genomic knowledge of oomycete pathogenicity is essential to gain the full context of how these pathogens cause disease on plants. An intense research focus on secreted Phytophthora effector proteins, especially those containing a conserved N-terminal RXLR motif, has meant that most cell biological studies into Phytophthora diseases have focussed on the effectors and their host target proteins. While these effector studies have provided novel insights into effector secretion and host defence mechanisms, there remain many unanswered questions about fundamental processes involved in spore biology, host penetration and haustorium formation and function.

Dehydration-induced alterations in chloroplast proteome and reprogramming of cellular metabolism in developing chickpea delineate interrelated adaptive responses

Chloroplast, the energy organelle unique to photosynthetic eukaryotes, executes several crucial functions including photosynthesis. While chloroplast development and function are controlled by the nucleus, environmental stress modulated alterations perceived by the chloroplasts are communicated to the nucleus via retrograde signaling. Notably, coordination of chloroplast and nuclear gene expression is synchronized by anterograde and retrograde signaling. The chloroplast proteome holds significance for stress responses and adaptation. We unraveled dehydration-induced alterations in the chloroplast proteome of a grain legume, chickpea and identified an array of dehydration-responsive proteins (DRPs) primarily involved in photosynthesis, carbohydrate metabolism and stress response. Notably, 12 DRPs were encoded by chloroplast genome, while the rest were nuclear-encoded. We observed a coordinated expression of different multi-subunit protein complexes viz., RuBisCo, photosystem II and cytochrome b6f, encoded by both chloroplast and nuclear genome. Comparison with previously reported stress-responsive chloroplast proteomes showed unique and overlapping components. Transcript abundance of several previously reported markers of retrograde signaling revealed relay of dehydration-elicited signaling events between chloroplasts and nucleus. Additionally, dehydration-triggered metabolic adjustments demonstrated alterations in carbohydrate and amino acid metabolism. This study offers a panoramic catalogue of dehydration-responsive signatures of chloroplast proteome and associated retrograde signaling events, and cellular metabolic reprograming.

Comparative transcriptome analysis of Zea mays in response to petroleum hydrocarbon stress

The use of plants for the improvement of soils contaminated with hydrocarbons has been a primary research focus in phytoremediation studies. Obtaining insights regarding genes that are differentially induced by petroleum hydrocarbon stress and understanding plant response mechanisms against petroleum hydrocarbons at molecular level is essential for developing better phytoremediation strategies to remove these hazardous contaminants. The purpose of this study was to analyze the transcriptomal profile changes under hydrocarbon stress in maize plants and identify the genes associated with the phytoremediative capacity. Zea mays GeneChips were used to analyze the global transcriptome profiles of maize treated with different concentrations of petroleum hydrocarbons. In total, 883, 1281, and 2162 genes were differentially induced or suppressed in the comparisons of 0 (control) vs. 1% crude petroleum, 1 vs. 5% crude petroleum, and 0 vs. 5% crude petroleum, respectively. The differentially expressed genes were functionally associated with the osmotic stress response mechanism, likely preventing the uptake of water from the roots, and the phytoremediative capacity of plants, e.g., secretory pathway genes. The results presented here show the regulatory mechanisms in the response to petroleum hydrocarbon pollution in soil. Our study provides global gene expression data of Z. mays in response to petroleum hydrocarbon stress that could be useful for further studies investigating the biodegradation mechanism in maize and other plants.

Identification of Genes Involved in the Responses of Tangor (C. reticulata × C. sinensis) to Drought Stress

Drought is the major abiotic stress with adverse effects on citrus, decreasing the agronomical yield and influencing the fruit quality. In this study, cDNA-amplified fragment length polymorphism (cDNA-AFLP) technique was used to investigate the transcriptional profile changes and identify drought-responsive genes in “Amakusa” tangor (C. reticulata × C. sinensis), a hybrid citrus sensitive to water stress. The 255 out of 6,245 transcript-derived fragments (TDFs) displayed altered expression patterns including (A) induction, (B) repression, (C) upregulation, and (D) downregulation. With BLAST search, the gene products of differentially expressed fragments (DEFs) could be classified into several categories: cellular processes, transcription, transport, metabolism, stress/stimuli response, and developmental processes. Downregulated genes were highly represented by photosynthesis and basic metabolism, while upregulated ones were enriched in genes that were involved in transcription regulation, defense, energy, and transport. Present result also revealed some transient and up- and then downregulated genes such as aquaporin protein and photosystem enzyme. Expression patterns of 17 TDFs among 18 homologous to function-known genes were confirmed by qRT-PCR analysis. The present results revealed potential mechanism of drought tolerance in fruit crop and also provided candidate genes for future experiments in citrus.

Comparative proteomic analyses reveal the proteome response to short-term drought in Italian ryegrass (Lolium multiflorum)

Drought is a major abiotic stress that impairs growth and productivity of Italian ryegrass. Comparative analysis of drought responsive proteins will provide insight into molecular mechanism in Lolium multiflorum drought tolerance. Using the iTRAQ-based approach, proteomic changes in tolerant and susceptible lines were examined in response to drought condition. A total of 950 differentially accumulated proteins was found to be involved in carbohydrate metabolism, amino acid metabolism, biosynthesis of secondary metabolites, and signal transduction pathway, such as β-D-xylosidase, β-D-glucan glucohydrolase, glycerate dehydrogenase, Cobalamin-independent methionine synthase, glutamine synthetase 1a, Farnesyl pyrophosphate synthase, diacylglycerol, and inositol 1, 4, 5-trisphosphate, which might contributed to enhance drought tolerance or adaption in Lolium multiflorum. Interestingly, the two specific metabolic pathways, arachidonic acid and inositol phosphate metabolism including differentially accumulated proteins, were observed only in the tolerant lines. Cysteine protease cathepsin B, Cysteine proteinase, lipid transfer protein and Aquaporin were observed as drought-regulated proteins participating in hydrolysis and transmembrane transport. The activities of phospholipid hydroperoxide glutathione peroxidase, peroxiredoxin, dehydroascorbate reductase, peroxisomal ascorbate peroxidase and monodehydroascorbate reductase associated with alleviating the accumulation of reactive oxygen species in stress inducing environments. Our results showed that drought-responsive proteins were closely related to metabolic processes including signal transduction, antioxidant defenses, hydrolysis, and transmembrane transport.

Profiling of drought-responsive microRNA and mRNA in tomato using high-throughput sequencing

BACKGROUND

Abiotic stresses cause severe loss of crop production. Among them, drought is one of the most frequent environmental stresses, which limits crop growth, development and productivity. Plant drought tolerance is fine-tuned by a complex gene regulatory network. Understanding the molecular regulation of this polygenic trait is crucial for the eventual success to improve plant yield and quality. Recent studies have demonstrated that microRNAs play critical roles in plant drought tolerance. However, little is known about the microRNA in drought response of the model plant tomato. Here, we described the profiling of drought-responsive microRNA and mRNA in tomato using high-throughput next-generation sequencing.

RESULTS

Drought stress was applied on the seedlings of M82, a drought-sensitive cultivated tomato genotype, and IL9-1, a drought-tolerant introgression line derived from the stress-resistant wild species Solanum pennellii LA0716 and M82. Under drought, IL9-1 performed superior than M82 regarding survival rate, H2O2 elimination and leaf turgor maintenance. A total of four small RNA and eight mRNA libraries were constructed and sequenced using Illumina sequencing technology. 105 conserved and 179 novel microRNAs were identified, among them, 54 and 98 were differentially expressed upon drought stress, respectively. The majority of the differentially-expressed conserved microRNAs was up-regulated in IL9-1 whereas down-regulated in M82. Under drought stress, 2714 and 1161 genes were found to be differentially expressed in M82 and IL9-1, respectively, and many of their homologues are involved in plant stress, such as genes encoding transcription factor and protein kinase. Various pathways involved in abiotic stress were revealed by Gene Ontology and pathway analysis. The mRNA sequencing results indicated that most of the target genes were regulated by their corresponding microRNAs, which suggested that microRNAs may play essential roles in the drought tolerance of tomato.

CONCLUSION

In this study, numerous microRNAs and mRNAs involved in the drought response of tomato were identified using high-throughput sequencing, which will provide new insights into the complex regulatory network of plant adaption to drought stress. This work will also help to exploit new players functioning in plant drought-stress tolerance.

A triticale water-deficit-inducible phytocystatin inhibits endogenous cysteine proteinases in vitro

Water-deficit is accompanied by an increase in proteolysis. Phytocystatins are plant inhibitors of cysteine proteinases that belong to the papain and legumain family. A cDNA encoding the protein inhibitor TrcC-8 was identified in the vegetative organs of triticale. In response to water-deficit, increases in the mRNA levels of TrcC-8 were observed in leaf and root tissues. Immunoblot analysis indicated that accumulation of the TrcC-8 protein occurred after 72h of water-deficit in the seedlings. Using recombinant protein, inhibitory activity of TrcC-8 against cysteine proteases from triticale and wheat tissues was analyzed. Under water-deficit conditions, there are increases in cysteine proteinase activities in both plant tissues. The cysteine proteinase activities were inhibited by addition of the recombinant TrcC-8 protein. These results suggest a potential role for the triticale phytocystatin in modulating cysteine proteinase activities during water-deficit conditions.

C1A cysteine protease-cystatin interactions in leaf senescence

Senescence-associated proteolysis in plants is a crucial process to relocalize nutrients from leaves to growing or storage tissues. The massive net degradation of proteins involves broad metabolic networks, different subcellular compartments, and several types of proteases and regulators. C1A cysteine proteases, grouped as cathepsin L-, B-, H-, and F-like according to their gene structures and phylogenetic relationships, are the most abundant enzymes responsible for the proteolytic activity during leaf senescence. Besides, cystatins as specific modulators of C1A peptidase activities exert a complex regulatory role in this physiological process. This overview article covers the most recent information on C1A proteases in leaf senescence in different plant species. Particularly, it is focussed on barley, as the unique species where the whole gene family members of C1A cysteine proteases and cystatins have been analysed.

Induction of a ricinosomal-protease and programmed cell death in tomato endosperm by gibberellic acid

Several examples of programmed cell death (PCD) in plants utilize ricinosomes, organelles that appear prior to cell death and store inactive KDEL-tailed cysteine proteinases. Upon cell death, the contents of ricinosomes are released into the cell corpse where the proteinases are activated and proceed to degrade any remaining protein for use in adjacent cells or, in the case of nutritive seed tissues, by the growing seedling. Ricinosomes containing pro-SlCysEP have been observed in anther tissues prior to PCD and ricinosome-like structures have been observed in imbibed seeds within endosperm cells of tomato. The present study confirms that the structures in tomato endosperm cells contain pro-SlCysEP making them bona fide ricinosomes. The relative abundance of pro- versus mature SlCysEP is suggested to be a useful indicator of the degree of PCD that has occurred in tomato endosperm, and is supported by biochemical and structural data. This diagnostic tool is used to demonstrate that a sub-region of the micropylar endosperm surrounding the emerged radical is relatively long-lived and may serve to prevent loss of mobilized reserves from the lateral endosperm. We also demonstrate that GA-induced reserve mobilization, SlCysEP accumulation and processing, and PCD in tomato endosperm are antagonized by ABA.

Serpin protease inhibitors in plant biology

Protease inhibitors of the serpin family are ubiquitous in the plant kingdom but relatively little is known about their biological functions in comparison with their counterparts in animals. X-ray crystal structures have provided crucial insights into animal serpin functions. The recently solved structure of AtSerpin1 from Arabidopsis thaliana, which has the highly conserved reactive center P2-P1' Leu-Arg-Xaa (Xaa = small residue), displays both conserved and plant-specific serpin features. Sequence homology suggests that AtSerpin1 belongs to serpin Clade B, composed of intracellular mammalian serpins, which is consistent with the lack of strong evidence for secretion of serpins from plant cells. The major in vivo target protease for AtSerpin1 is the papain-like cysteine RD21 protease, a match reminiscent of the inhibition of cathepsins K, L and S by the Clade-B mammalian serpin, SCCA-1 (SERPINB3). The function of AtSerpin1 and other serpins that contain P2-P1' Leu-Arg-Xaa (the 'LR' serpins) in plants remains unknown. However, based on its homology and interactive partners, AtSerpin1 and perhaps other serpins are likely to be involved in regulating programmed cell death or associated processes such as senescence. Abundant accumulation of serpins in seeds and their presence in phloem sap suggest additional functions in plant defense by irreversible inhibition of digestive proteases from pests or pathogens. Here we review the most recent findings in plant serpin biology, focusing on advances in describing the structure and inhibitory specificity of the LR serpins.

A role in immunity for Arabidopsis cysteine protease RD21, the ortholog of the tomato immune protease C14

Secreted papain-like Cys proteases are important players in plant immunity. We previously reported that the C14 protease of tomato is targeted by cystatin-like EPIC proteins that are secreted by the oomycete pathogen Phytophthora infestans (Pinf) during infection. C14 has been under diversifying selection in wild potato species coevolving with Pinf and reduced C14 levels result in enhanced susceptibility for Pinf. Here, we investigated the role C14-EPIC-like interactions in the natural pathosystem of Arabidopsis with the oomycete pathogen Hyaloperonospora arabidopsidis (Hpa). In contrast to the Pinf-solanaceae pathosystem, the C14 orthologous protease of Arabidopsis, RD21, does not evolve under diversifying selection in Arabidopsis, and rd21 null mutants do not show phenotypes upon compatible and incompatible Hpa interactions, despite the evident lack of a major leaf protease. Hpa isolates express highly conserved EPIC-like proteins during infections, but it is unknown if these HpaEPICs can inhibit RD21 and one of these HpaEPICs even lacks the canonical cystatin motifs. The rd21 mutants are unaffected in compatible and incompatible interactions with Pseudomonas syringae pv. tomato, but are significantly more susceptible for the necrotrophic fungal pathogen Botrytis cinerea, demonstrating that RD21 provides immunity to a necrotrophic pathogen.

Phytophthora infestans effector AVRblb2 prevents secretion of a plant immune protease at the haustorial interface

In response to pathogen attack, plant cells secrete antimicrobial molecules at the site of infection. However, how plant pathogens interfere with defense-related focal secretion remains poorly known. Here we show that the host-translocated RXLR-type effector protein AVRblb2 of the Irish potato famine pathogen Phytophthora infestans focally accumulates around haustoria, specialized infection structures that form inside plant cells, and promotes virulence by interfering with the execution of host defenses. AVRblb2 significantly enhances susceptibility of host plants to P. infestans by targeting the host papain-like cysteine protease C14 and specifically preventing its secretion into the apoplast. Plants altered in C14 expression were significantly affected in susceptibility to P. infestans in a manner consistent with a positive role of C14 in plant immunity. Our findings point to a unique counterdefense strategy that plant pathogens use to neutralize secreted host defense proteases. Effectors, such as AVRblb2, can be used as molecular probes to dissect focal immune responses at pathogen penetration sites.

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.

An effector-targeted protease contributes to defense against Phytophthora infestans and is under diversifying selection in natural hosts

Since the leaf apoplast is a primary habitat for many plant pathogens, apoplastic proteins are potent, ancient targets for apoplastic effectors secreted by plant pathogens. So far, however, only a few apoplastic effector targets have been identified and characterized. Here, we discovered that the papain-like cysteine protease C14 is a new common target of EPIC1 and EPIC2B, two apoplastic, cystatin-like proteins secreted by the potato (Solanum tuberosum) late blight pathogen Phytophthora infestans. C14 is a secreted protease of tomato (Solanum lycopersicum) and potato typified by a carboxyl-terminal granulin domain. The EPIC-C14 interaction occurs at a wide pH range and is stronger than the previously described interactions of EPICs with tomato defense proteases PIP1 and RCR3. The selectivity of the EPICs is also different when compared with the AVR2 effector of the fungal tomato pathogen Cladosporium fulvum, which targets PIP1 and RCR3, and only at apoplastic pH. Importantly, silencing of C14 increased susceptibility to P. infestans, demonstrating that this protease plays a role in pathogen defense. Although C14 is under conservative selection in tomato, it is under diversifying selection in wild potato species (Solanum demissum, Solanum verrucosum, and Solanum stoliniferum) that are the natural hosts of P. infestans. These data reveal a novel effector target in the apoplast that contributes to immunity and is under diversifying selection, but only in the natural host of the pathogen.

Differences in root functions during long-term drought adaptation: comparison of active gene sets of two wheat genotypes

In an attempt to shed light on the role of root systems in differential responses of wheat genotypes to long-term water limitation, transcriptional differences between two wheat genotypes (Triticum aestivum L., cv. Plainsman V and landrace Kobomugi) were identified during adaptation to moderate water stress at the tillering stage. Differences in organ sizes, water-use efficiency and seed production were detected in plants grown in soil, and root functions were characterised by expression profiling. The molecular genetic background of the behaviour of the two genotypes during this stress was revealed using a cDNA macroarray for transcript profiling of the roots. During a 4-week period of moderate water deficit, a set of up-regulated genes displaying transiently increased expression was identified in young plantlets, mostly in the second week in the roots of Kobomugi, while transcript levels remained constantly high in roots of Plainsman V. These genes encode proteins with various functions, such as transport, protein metabolism, osmoprotectant biosynthesis, cell wall biogenesis and detoxification, and also regulatory proteins. Oxidoreductases, peroxidases and cell wall-related genes were induced significantly only in Plainsman V, while induction of stress- and defence-related genes was more pronounced in Kobomugi. Real-time qPCR analysis of selected members of the glutathione S-transferase gene family revealed differences in regulation of family members in the two genotypes and confirmed the macroarray results. The TaGSTZ gene was stress-activated only in the roots of Kobomugi.

Isolation and characterization of osmotic stress-induced genes in poplar cells by suppression subtractive hybridization and cDNA microarray analysis

Osmotic stress induces changes in the expression of various genes including those associated with drought tolerance, cell wall metabolism and defense. We isolated 852 cDNA clones, the expression of which is induced by osmotic stress, from cells of a hybrid poplar (Populus alba x Populus tremula var. glandulosa) by suppression subtractive hybridization after mannitol treatment. We examined how stress affected their expression using cDNA microarray analysis, which identified 104 genes significantly up-regulated by osmotic stress. These include genes with functions related to transcription, signal transduction, cell wall metabolism and defense. Other gene transcripts encoding cysteine protease and aquaporin are also up-regulated during osmotic stress. The function of about one-third of the genes in poplar cells that were significantly up-regulated by stress is not known, suggesting that the cell suspension may offer an opportunity of finding novel genes otherwise never expressed and that we still need more information at the molecular level.

Construction and analysis of cotton (Gossypium arboreum L.) drought-related cDNA library

Background

Drought is one of the most important environmental factors causing water stress for cotton, and it greatly limits cotton growth and crop productivity. So far only a few drought-tolerance genes have been functionally characterized in details, and most efforts on this topic have been made in model organisms. Therefore, to identify more drought-related genes in cotton plays a crucial role in elucidating the underlying mechanisms of drought tolerance as well as utilizing bioengineering techniques to improve the tolerance in this organism.

Findings

Here we constructed a subtractive drought-tolerance cDNA library using suppressive subtractive hybridization (SSH). Through differential screening and bioinformatics analysis, we identified 392 positive clones with differential expression, corresponding 265 unique genes. By BLAST search against Genbank, we found that more than half of these EST sequences were homologous to those previously known drought-related genes and that there were 57 sequences with unknown functions, suggesting that many more genes are involved in this complex trait. Moreover, using RT-PCR, we examined the expression of nine representative candidate genes and confirmed that their expression levels were increased at different levels under drought stress.

Conclusion

Our results show that drought tolerance is a complex trait in cotton, which involves the coordination of many genes and multiple metabolism pathways. The candidate EST sequences we identified here would facilitate further functional studies of drought-related genes and provide important insights into the molecular mechanisms of drought-stress tolerance and genetic breeding in cotton.

Biochemical analysis of a papain-like protease isolated from the latex of Asclepias curassavica L

Most of the species belonging to Asclepiadaceae family usually secrete an endogenous milk-like fluid in a network of laticifer cells in which sub-cellular organelles intensively synthesize proteins and secondary metabolites. A new papain-like endopeptidase (asclepain c-II) has been isolated and characterized from the latex extracted from petioles of Asclepias curassavica L. (Asclepiadaceae). Asclepain c-II was the minor proteolytic component in the latex, but showed higher specific activity than asclepain c-I, the main active fraction previously studied. Both enzymes displayed quite distinct biochemical characteristics, confirming that they are different enzymes. Crude extract was purified by cation exchange chromatography (FPLC). Two active fractions, homogeneous by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and mass spectrometry, were isolated. Asclepain c-II displayed a molecular mass of 23,590 Da, a pI higher than 9.3, maximum proteolytic activity at pH 9.4-10.2, and showed poor thermostability. The activity of asclepain c-II is inhibited by cysteine proteases inhibitors like E-64, but not by any other protease inhibitors such as 1,10-phenantroline, phenylmethanesulfonyl fluoride, and pepstatine. The Nterminal sequence (LPSFVDWRQKGVVFPIRNQGQCGSCWTFSA) showed a high similarity with those of other plant cysteine proteinases. When assayed on N-alpha-CBZ-amino acid-p-nitrophenyl esters, the enzyme exhibited higher preference for the glutamine derivative. Determinations of kinetic parameters were performed with N-alpha-CBZ-L-Gln-p-nitrophenyl ester as substrate: K(m)=0.1634 mM, k(cat)=121.48 s(-1), and k(cat)/K(m)=7.4 x 10(5) s(-1)/mM.

Biochemical and proteomic analysis of 'Dixiland' peach fruit (Prunus persica) upon heat treatment

Shipping of peaches to distant markets and storage require low temperature; however, cold storage affects fruit quality causing physiological disorders collectively termed 'chilling injury' (CI). In order to ameliorate CI, different strategies have been applied before cold storage; among them heat treatment (HT) has been widely used. In this work, the effect of HT on peach fruit quality as well as on carbon metabolism was evaluated. When fruit were exposed to 39 degrees C for 3 d, ripening was delayed, with softening inhibition and slowing down of ethylene production. Several differences were observed between fruit ripening at ambient temperature versus fruit that had been heat treated. However, the major effects of HT on carbon metabolism and organoleptic characteristics were reversible, since normal fruit ripening was restored after transferring heated peaches to ambient temperature. Positive quality features such as an increment in the fructose content, largely responsible for the sweetness, and reddish coloration were observed. Nevertheless, high amounts of acetaldehyde and low organic acid content were also detected. The differential proteome of heated fruit was characterized, revealing that heat-induced CI tolerance may be acquired by the activation of different molecular mechanisms. Induction of related stress proteins in the heat-exposed fruits such as heat shock proteins, cysteine proteases, and dehydrin, and repression of a polyphenol oxidase provide molecular evidence of candidate proteins that may prevent some of the CI symptoms. This study contributes to a deeper understanding of the cellular events in peach under HT in view of a possible technological use aimed to improve organoleptic and shelf-life features.

RD19, an Arabidopsis cysteine protease required for RRS1-R-mediated resistance, is relocalized to the nucleus by the Ralstonia solanacearum PopP2 effector

Bacterial wilt, a disease impacting cultivated crops worldwide, is caused by the pathogenic bacterium Ralstonia solanacearum. PopP2 (for Pseudomonas outer protein P2) is an R. solanacearum type III effector that belongs to the YopJ/AvrRxv protein family and interacts with the Arabidopsis thaliana RESISTANT TO RALSTONIA SOLANACEARUM 1-R (RRS1-R) resistance protein. RRS1-R contains the Toll/Interleukin1 receptor-nucleotide binding site-Leu-rich repeat domains found in several cytoplasmic R proteins and a C-terminal WRKY DNA binding domain. In this study, we identified the Arabidopsis Cys protease RESPONSIVE TO DEHYDRATION19 (RD19) as being a PopP2-interacting protein whose expression is induced during infection by R. solanacearum. An Arabidopsis rd19 mutant in an RRS1-R genetic background is compromised in resistance to the bacterium, indicating that RD19 is required for RRS1-R-mediated resistance. RD19 normally localizes in mobile vacuole-associated compartments and, upon coexpression with PopP2, is specifically relocalized to the plant nucleus, where the two proteins physically interact. No direct physical interaction between RRS1-R and RD19 in the presence of PopP2 was detected in the nucleus as determined by Förster resonance energy transfer. We propose that RD19 associates with PopP2 to form a nuclear complex that is required for activation of the RRS1-R-mediated resistance response.

The Cladosporium fulvum virulence protein Avr2 inhibits host proteases required for basal defense

Cladosporium fulvum (syn. Passalora fulva) is a biotrophic fungal pathogen that causes leaf mold of tomato (Solanum lycopersicum). During growth in the apoplast, the fungus establishes disease by secreting effector proteins, 10 of which have been characterized. We have previously shown that the Avr2 effector interacts with the apoplastic tomato Cys protease Rcr3, which is required for Cf-2-mediated immunity. We now show that Avr2 is a genuine virulence factor of C. fulvum. Heterologous expression of Avr2 in Arabidopsis thaliana causes enhanced susceptibility toward extracellular fungal pathogens, including Botrytis cinerea and Verticillium dahliae, and microarray analysis showed that Avr2 expression triggers a global transcriptome reflecting pathogen challenge. Cys protease activity profiling showed that Avr2 inhibits multiple extracellular Arabidopsis Cys proteases. In tomato, Avr2 expression caused enhanced susceptibility toward Avr2-defective C. fulvum strains and also toward B. cinerea and V. dahliae. Cys protease activity profiling in tomato revealed that, in this plant also, Avr2 inhibits multiple extracellular Cys proteases, including Rcr3 and its close relative Pip1. Finally, silencing of Avr2 significantly compromised C. fulvum virulence on tomato. We conclude that Avr2 is a genuine virulence factor of C. fulvum that inhibits several Cys proteases required for plant basal defense.

Plant programmed cell death: can't live with it; can't live without it

The decision of whether a cell should live or die is fundamental for the wellbeing of all organisms. Despite intense investigation into cell growth and proliferation, only recently has the essential and equally important idea that cells control/programme their own demise for proper maintenance of cellular homeostasis gained recognition. Furthermore, even though research into programmed cell death (PCD) has been an extremely active area of research there are significant gaps in our understanding of the process in plants. In this review, we discuss PCD during plant development and pathogenesis, and compare/contrast this with mammalian apoptosis.

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.

Fungal effector protein AVR2 targets diversifying defense-related cys proteases of tomato

The interaction between the fungal pathogen Cladosporium fulvum and its host tomato (Solanum lycopersicum) is an ideal model to study suppression of extracellular host defenses by pathogens. Secretion of protease inhibitor AVR2 by C. fulvum during infection suggests that tomato papain-like cysteine proteases (PLCPs) are part of the tomato defense response. We show that the tomato apoplast contains a remarkable diversity of PLCP activities with seven PLCPs that fall into four different subfamilies. Of these PLCPs, transcription of only PIP1 and RCR3 is induced by treatment with benzothiadiazole, which triggers the salicylic acid-regulated defense pathway. Sequencing of PLCP alleles of tomato relatives revealed that only PIP1 and RCR3 are under strong diversifying selection, resulting in variant residues around the substrate binding groove. The doubled number of variant residues in RCR3 suggests that RCR3 is under additional adaptive selection, probably to prevent autoimmune responses. AVR2 selectively inhibits only PIP1 and RCR3, and one of the naturally occurring variant residues in RCR3 affects AVR2 inhibition. The higher accumulation of PIP1 protein levels compared with RCR3 indicates that PIP1 might be the real virulence target of AVR2 and that RCR3 acts as a decoy for AVR2 perception in plants carrying the Cf-2 resistance gene.

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.

Identification and characterisation of acidic and novel basic forms of actinidin, the highly abundant cysteine protease from kiwifruit

Actinidin is a cysteine protease found in Actinidia Lindl. (kiwifruit) species that affects the nutraceutical properties, processing characteristics and allergenicity of the fruit. Given the increased consumption of kiwifruit worldwide and the release of new varieties from different Actinidia species, the expression of actinidin mRNA and protein in a range of kiwifruit tissues was examined. Ten different actinidin mRNAs were identified encoding mature proteins of similar molecular weight (~24 kDa), but with predicted pIs ranging from acidic (pI 3.9) to basic (pI 9.3). In A. deliciosa 'Hayward' (green-fleshed kiwifruit) and A. chinensis 'Hort16A' and EM4 (gold-fleshed kiwifruit), actinidin mRNAs for acidic and basic proteins were expressed at comparable levels throughout ripening. Actinidin mRNA expression was highest in fruit at harvest, expression decreased as fruit ripened and was much lower in the core compared with outer pericarp tissue. Two-dimensional gel electrophoresis, combined with western analysis and liquid chromatography mass spectrometry (LC-MS) identified low levels of a novel basic actinidin protein in ripe A. deliciosa and A. chinensis fruit. Extremely high levels of an acidic actinidin protein were detected in A. deliciosa fruit and EM4, but this acidic protein appeared to be absent in 'Hort16A', the most important commercial cultivar of A. chinensis. Analyses on native gels indicated that both the basic and acidic actinidin isoforms in A. deliciosa were active cysteine proteases. Immunolocalisation showed that actinidin was present in small cells, but not large cells in the outer pericarp of mature A. deliciosa fruit at harvest. Within the small cells, actinidin was localised diffusely in the vacuole, associated with the plasma membrane, and in a layer in the plastids near starch granules. The presence of multiple forms of actinidin and varying protein levels in fruit will impact on the ability to breed new kiwifruit varieties with altered actinidin levels.

Proteomic analysis of rice seedlings during cold stress

Low temperature is one of the important environmental changes that affect plant growth and agricultural production. To investigate the responses of rice to cold stress, changes in protein expression were analyzed using a proteomic approach. Two-week-old rice seedlings were exposed to 5 degrees C for 48 h, then total crude proteins were extracted from leaf blades, leaf sheaths and roots, separated by 2-DE and stained with CBB. Of the 250-400 protein spots from each organ, 39 proteins changed in abundance after cold stress, with 19 proteins increasing, and 20 proteins decreasing. In leaf blades, it was difficult to detect the changes in stress-responsive proteins due to the presence of an abundant protein, ribulose bisphosphate carboxylase/oxygenase large subunit (RuBisCO LSU), which accounted for about 50% of the total proteins. To overcome this problem, an antibody-affinity column was prepared to trap RuBisCO LSU, and the remaining proteins in the flow through from the column were subsequently separated using 2-DE. As a result, slight changes in stress responsive proteins were clearly displayed, and four proteins were newly detected after cold stress. From identified proteins, it was concluded that proteins related to energy metabolism were up-regulated, and defense-related proteins were down-regulated in leaf blades, by cold stress. These results suggest that energy production is activated in the chilling environment; furthermore, stress-related proteins are rapidly up-regulated, while defense-related proteins disappear, under long-term cold stress.

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.

Water deficit induces variation in expression of stress-responsive genes in two peanut (Arachis hypogaea L.) cultivars with different tolerance to drought

Peanut (Arachis hypogaea L.) is an important subsistence and cash crop in the semi-arid tropics where it often suffers from drought stress. Although its ecophysiological responses are studied, little is known about the molecular events involved in its adaptive responses to drought. The aim of this study was to investigate the involvement of membrane phospholipid and protein degrading enzymes as well as protective proteins such as "late embryogenesis-abundant" (LEA) protein in peanut adaptive responses to drought. Partial cDNAs encoding putative phospholipase D alpha, cysteine protease, serine protease and a full-length cDNA encoding a LEA protein were cloned. Their expression in response to progressive water deficit and rehydration was compared between cultivars differing in their tolerance to drought. Differential gene expression pattern according to either water deficit intensity and cultivar's tolerance to drought were observed. A good correspondence between the molecular responses of the studied cultivars and their physiological responses previously defined in greenhouse and field experiments was found. Molecular characters, as they were detectable at an early stage, could therefore be efficiently integrated in groundnut breeding programmes for drought adaptation. Thus, the relevance of the target genes as drought tolerance indicators is discussed.

Gradual soil water depletion results in reversible changes of gene expression, protein profiles, ecophysiology, and growth performance in Populus euphratica, a poplar growing in arid regions

The responses of Populus euphratica Oliv. plants to soil water deficit were assessed by analyzing gene expression, protein profiles, and several plant performance criteria to understand the acclimation of plants to soil water deficit. Young, vegetatively propagated plants originating from an arid, saline field site were submitted to a gradually increasing water deficit for 4 weeks in a greenhouse and were allowed to recover for 10 d after full reirrigation. Time-dependent changes and intensity of the perturbations induced in shoot and root growth, xylem anatomy, gas exchange, and water status were recorded. The expression profiles of approximately 6,340 genes and of proteins and metabolites (pigments, soluble carbohydrates, and oxidative compounds) were also recorded in mature leaves and in roots (gene expression only) at four stress levels and after recovery. Drought successively induced shoot growth cessation, stomatal closure, moderate increases in oxidative stress-related compounds, loss of CO2 assimilation, and root growth reduction. These effects were almost fully reversible, indicating that acclimation was dominant over injury. The physiological responses were paralleled by fully reversible transcriptional changes, including only 1.5% of the genes on the array. Protein profiles displayed greater changes than transcript levels. Among the identified proteins for which expressed sequence tags were present on the array, no correlation was found between transcript and protein abundance. Acclimation to water deficit involves the regulation of different networks of genes in roots and shoots. Such diverse requirements for protecting and maintaining the function of different plant organs may render plant engineering or breeding toward improved drought tolerance more complex than previously anticipated.

Molecular cloning and characterization of a granulin-containing cysteine protease SPCP3 from sweet potato (Ipomoea batatas) senescent leaves

Granulins are a family of evolutionarily ancient proteins that are involved in regulating cell growth and division in animals. In this report a full-length cDNA, SPCP3, was isolated from senescent leaves of sweet potato (Ipomoea batatas). SPCP3 contains 1389 nucleotides (462 amino acids) in its open reading frame, and exhibits high amino acid sequence homologies (ca. 64-73.6%) with several plant granulin-containing cysteine proteases, including potato, tomato, soybean, kidney bean, pea, maize, rice, cabbage, and Arabidopsis. Gene structural analysis shows that SPCP3 encodes a putative precursor protein. Via cleavage of the N-terminal propeptide, it generates a protein with 324 amino acids (from the 139th to the 462nd amino acid residues), which contains two main domains: the conserved catalytic domain with the putative catalytic residues (the 163rd Cys, 299th His and 319th Asn) and the C-terminal granulin domain (from the 375th to the 462nd amino acid residues). Semi-quantitative RT-PCR and protein gel blot hybridization showed that SPCP3 gene expression was enhanced significantly in natural senescent leaves and in dark- and ethephon-induced senescent leaves, but was almost undetectable in mature green leaves, veins, and roots. Phylogenic analysis showed that SPCP3 displayed close association with a group of plant granulin-containing cysteine proteases which have been implied to be involved in programmed cell death. In conclusion, sweet potato SPCP3 is a functional, senescence-associated gene. Its mRNA and protein levels were significantly enhanced in natural and induced senescing leaves. The physiological role and/or function of SPCP3 associated with programmed cell death during leaf senescence were also discussed.

A novel plant cysteine protease has a dual function as a regulator of 1-aminocyclopropane-1-carboxylic Acid synthase gene expression

The hormone ethylene influences plant growth, development, and some defense responses. The fungal elicitor Ethylene-Inducing Xylanase (EIX) elicits ethylene biosynthesis in tomato (Lycopersicon esculentum) and tobacco (Nicotiana tabacum) leaves by induction of 1-aminocyclopropane-1-caboxylic acid synthase (Acs) gene expression. A minimal promoter element in the LeAcs2 gene required for EIX responsiveness was defined by deletion analysis in transgenic tomato plants. The sequence between -715 and -675 of the tomato Acs2 gene was found to be essential for induction by EIX. A Cys protease (LeCp) was isolated that specifically binds to this cis element in vitro. Ectopic expression of LeCp in tomato leaves induced the expression of Acs2. Moreover, chromatin immunoprecipitation showed that LeCp binds in vivo to the Acs promoter. We propose a mechanism for the dual function of the LeCp protein. The protease acts enzymatically in the cytoplasm. Then, upon signaling, a small ubiquitin-related modifier protein binds to it, enabling entrance into the nucleus, where it acts as a transcription factor. Thus, LeCp can be considered a dual-function protein, having enzymatic activity and, upon elicitor signaling, exhibiting transcriptional factor activity that induces LeAcs2 expression.

Leaf senescence: signals, execution, and regulation

Leaf senescence is a type of postmitotic senescence. The onset and progression of leaf senescence are controlled by an array of external and internal factors including age, levels of plant hormones/growth regulators, and reproductive growth. Many environmental stresses and biological insults such as extreme temperature, drought, nutrient deficiency, insufficient light/shadow/darkness, and pathogen infection can induce senescence. Perception of signals often leads to changes in gene expression, and the upregulation of thousands of senescence-associated genes (SAGs) causes the senescence syndrome: decline in photosynthesis, degradation of macromolecules, mobilization of nutrients, and ultimate cell death. Identification and analysis of SAGs, especially genome-scale investigations on gene expression during leaf senescence, make it possible to decipher the molecular mechanisms of signal perception, execution, and regulation of the leaf senescence process. Biochemical and metabolic changes during senescence have been elucidated, and potential components in signal transduction such as receptor-like kinases and MAP kinase cascade have been identified. Studies on some master regulators such as WRKY transcription factors and the senescence-responsive cis element of the senescence-specific SAG12 have shed some light on transcriptional regulation of leaf senescence.

Sugar-responsive gene expression, invertase activity, and senescence in aborting maize ovaries at low water potentials

BACKGROUND AND AIMS

Ovary abortion can occur in maize (Zea mays) if water deficits lower the water potential (psiw) sufficiently to inhibit photosynthesis around the time of pollination. The abortion decreases kernel number. The present work explored the activity of ovary acid invertases and their genes, together with other genes for sucrose-processing enzymes, when this kind of abortion occurred. Cytological evidence suggested that senescence may have been initiated after 2 or 3 d of low psiw, and the expression of some likely senescence genes was also determined.

METHODS

Ovary abortion was assessed at kernel maturity. Acid invertase activities were localized in vivo and in situ. Time courses for mRNA abundance were measured with real time PCR. Sucrose was fed to the stems to vary the sugar flux.

KEY RESULTS

Many kernels developed in controls but most aborted when psiw became low. Ovary invertase was active in controls but severely inhibited at low psiw for cell wall-bound forms in vivo and soluble forms in situ. All ovary genes for sucrose processing enzymes were rapidly down-regulated at low psiw except for a gene for invertase inhibitor peptide that appeared to be constitutively expressed. Some ovary genes for senescence were subsequently up-regulated (RIP2 and PLD1). In some genes, these regulatory changes were reversed by feeding sucrose to the stems. Abortion was partially prevented by feeding sucrose.

CONCLUSIONS

A general response to low psiw in maize ovaries was an early down-regulation of genes for sucrose processing enzymes followed by up-regulation of some genes involved in senescence. Because some of these genes were sucrose responsive, the partial prevention of abortion with sucrose feeding may have been caused in part by the differential sugar-responsiveness of these genes. The late up-regulation of senescence genes may have caused the irreversibility of abortion.

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.

Characterization of senescence-associated proteases in postharvest broccoli florets

We characterized the senescence-associated proteases of postharvest broccoli (Brassica oleracea L. var Green King) florets, using class-specific protease inhibitors and gelatin-polyacrylamide gel electrophoresis. Different classes of senescence-associated proteases in broccoli florets were partially characterized for the first time. Protease activity of broccoli florets was depressed by all the inhibitors and showed different inhibition curves during postharvest. The hydrolytic activity of metalloprotease (EC 3.4.24. - ) and serine protease (EC 3.4.21. - ) reached a maximum, 1 day after harvest (DAH), then decreased, while the hydrolytic activity of cysteine protease (EC 3.4.22. - ) and aspartic protease (EC 3.4.23. - ) increased throughout the postharvest senescence based on the calculated inhibition percentage of protease activity. The senescence-associated proteases were separated into seven endoprotease (EP) groups by gelatin-polyacryamide gel electrophoresis and classified into EP1 (metalloprotease), EP2 (metalloprotease and cysteine protease), EP3 (serine protease and aspartic protease), EP4, EP5, EP7 (cysteine protease), and EP6 (serine protease) based on the sensitivity of class-specific protease inhibitors. The proteases EP2, EP3, and EP4 were present throughout the postharvest stages. EP3 was the major EP at all times during senescence; EP4 intensity of activity increased after 2 DAH; EP6 and EP7 clearly increased after 4 DAH. Our results suggest that serine protease activity contributes to early stage (0-1 DAH) and late stage (4-5 DAH) of senescence; metalloprotease activity was involved in the early and intermediate stages (0-3 DAH) of senescence; and cysteine protease and aspartic protease activities participated in the whole process of broccoli senescence.

Three-dimensional progression of programmed death in the rice coleoptile

Plant death during development is a highly orchestrated process at the cellular, tissue, organ, and whole-plant levels. The process toward death is endogenously programmed in plants. With our original approach called "three-dimensional analysis" using the rice coleoptile, we revealed detailed morphological alterations in the progression of senescence and programmed cell death involved in the air space (aerenchyma) formation at both tissue and cellular levels. Although these two types of cell death exhibited a distinct pattern of progression at the tissue level, the set of intracellular events was highly conserved. From those comprehensive investigations, we hypothesized that the identical program of death functions in each process of cell death, and that the initiation and progression of cell death is highly regulated by the environmental input.