Induction of competence for elicitation of defense responses in cucumber hypocotyls requires proteasome activity

Conformational Changes in Three-Dimensional Chromatin Structure in Paulownia fortunei After Phytoplasma Infection

Higher-order chromatin structures play important roles in regulating multiple biological processes such as growth and development as well as biotic and abiotic stress response. However, little is known about three-dimensional chromatin structures in Paulownia or about whole-genome chromatin conformational changes that occur in response to Paulownia witches' broom (PaWB) disease. We used high-throughput chromosome conformation capture (Hi-C) to obtain genome-wide profiles of chromatin conformation in both healthy and phytoplasma-infected Paulownia fortunei genome. The heat map results indicated that the strongest interactions between chromosomes were in the telomeres. We confirmed that the main structural characteristics of A/B compartments, topologically associated domains, and chromatin loops were prominent in the Paulownia genome and were clearly altered in phytoplasma-infected plants. By combining chromatin immunoprecipitation sequencing, Hi-C signals, and RNA sequencing data, we inferred that the chromatin structure changed and the modification levels of three histones (H3K4me3/K9ac/K36me3) increased in phytoplasma-infected P. fortunei, which was associated with changes of transcriptional activity. We concluded that for epigenetic modifications, transcriptional activity might function in combination to shape chromatin packing in healthy and phytoplasm-infected Paulownia. Finally, 11 genes (e.g., RPN6, Sec61 subunit-α) that were commonly located at specific topologically associated domain boundaries, A/B compartment switching and specific loops, and had been associated with histone marks were identified and considered as closely related to PaWB stress. Our results provide new insights into the nexus between gene regulation and chromatin conformational alterations in nonmodel plants upon phytopathogen infection and plant disease resistance.

Protective Roles of Cytosolic and Plastidal Proteasomes on Abiotic Stress and Pathogen Invasion

Protein malfunction is typically caused by abiotic stressors. To ensure cell survival during conditions of stress, it is important for plant cells to maintain proteins in their respective functional conformation. Self-compartmentalizing proteases, such as ATP-dependent Clp proteases and proteasomes are designed to act in the crowded cellular environment, and they are responsible for degradation of misfolded or damaged proteins within the cell. During different types of stress conditions, the levels of misfolded or orphaned proteins that are degraded by the 26S proteasome in the cytosol and nucleus and by the Clp proteases in the mitochondria and chloroplasts increase. This allows cells to uphold feedback regulations to cellular-level signals and adjust to altered environmental conditions. In this review, we summarize recent findings on plant proteolytic complexes with respect to their protective functions against abiotic and biotic stressors.

Tomato 26S Proteasome subunit RPT4a regulates ToLCNDV transcription and activates hypersensitive response in tomato

Involvement of 26S proteasomal subunits in plant pathogen-interactions, and the roles of each subunit in independently modulating the activity of many intra- and inter-cellular regulators controlling physiological and defense responses of a plant were well reported. In this regard, we aimed to functionally characterize a Solanum lycopersicum 26S proteasomal subunit RPT4a (SlRPT4) gene, which was differentially expressed after Tomato leaf curl New Delhi virus (ToLCNDV) infection in tolerant cultivar H-88-78-1. Molecular analysis revealed that SlRPT4 protein has an active ATPase activity. SlRPT4 could specifically bind to the stem-loop structure of intergenic region (IR), present in both DNA-A and DNA-B molecule of the bipartite viral genome. Lack of secondary structure in replication-associated gene fragment prevented formation of DNA-protein complex suggesting that binding of SlRPT4 with DNA is secondary structure specific. Interestingly, binding of SlRPT4 to IR inhibited the function of RNA Pol-II and subsequently reduced the bi-directional transcription of ToLCNDV genome. Virus-induced gene silencing of SlRPT4 gene incited conversion of tolerant attributes of cultivar H-88-78-1 into susceptibility. Furthermore, transient overexpression of SlRPT4 resulted in activation of programmed cell death and antioxidant enzymes system. Overall, present study highlights non-proteolytic function of SlRPT4 and their participation in defense pathway against virus infection in tomato.

Comparative proteomic analysis of β-aminobutyric acid-mediated alleviation of salt stress in barley

The non-protein amino acid β-aminobutyric acid (BABA) is known to induce plant resistance to a broad spectrum of biotic and abiotic stresses. This is the first study describing the effect of BABA seed priming on physiological and proteomic changes under salt stress conditions in barley (Hordeum vulgare). The aim of our study was to investigate the changes of fresh weight, dry weight and relative water content (RWC) as well as root proteome changes of two barley lines contrasting in salt tolerance (DH14, DH 187) in response to salt stress after seed priming in water or in 800 μM BABA. Seed priming with BABA significantly increased (p ≤ 0.05) RWC in both barley lines, which indicates considerably lower water loss in BABA-primed plants than in the non-primed control plants. Dry and fresh matter increased significantly in line DH 187, whereas no changes were detected in line DH14. BABA-primed plants of both lines showed different proteomic patterns than the non-primed control plants. The root proteins exhibiting significant abundance changes (1.75-fold change, p ≤ 0.05) were separated by two-dimensional polyacrylamide gel electrophoresis (2D- PAGE). Thirty-one spots, representing 24 proteins, were successfully identified by MALDI TOF/TOF mass spectrometry. The most prominent differences include the up-regulation of antioxidant enzymes (catalase, peroxidase and superoxide dismutase), PR proteins (chitinase, endo-1,3-β-glucosidase), and chaperones (cyclophilin, HSC 70). Our results indicate that BABA induces defence and detoxification processes which may enable faster and more effective responses to salt stress, increasing the chances of survival under adverse environmental conditions.

Tomato susceptibility to Fusarium crown and root rot: effect of grafting combination and proteomic analysis of tolerance expression in the rootstock

Grafting can enhance the tolerance of vegetable crops to soilborne diseases. The aim of this study was to investigate whether different tomato scion-rootstock combinations may affect the plant susceptibility to Fusarium oxysporum f. sp. radicis-lycopersici (FORL), the causal agent of crown and root rot. A proteomic approach was used to investigate whenever the protein repertoire of the rootstock can be modified by FORL infection, in relation to cultivar susceptibility/tolerance to the disease. To this purpose, plants of tomato hybrids with different vigor, "Costoluto Genovese" (less vigorous) and "Kadima" (more vigorous), were grafted onto "Cuore di Bue" and "Natalia" hybrids, sensitive and tolerant versus FORL infections, respectively. Disease symptoms, plant biomasses, and protein expression patterns were evaluated 45 days after FORL inoculation. The extent of vascular discoloration caused by FORL in tomato plants grafted on "Natalia" rootstock (0.12-0.37 cm) was significantly lower than that of plants grafted on sensitive "Cuore di Bue" (1.75-6.50 cm). FORL symptoms significantly differed between "Costoluto Genovese" and "Kadima" scions only when grafted on sensitive rootstock. Shoot FW of non-inoculated "Kadima"/"Cuore di Bue" combination was 35% lower than "Kadima"/"Natalia", whereas no difference was manifested in inoculated plants. Shoot FW of inoculated "Costoluto Genovese"/"Cuore di Bue" combination was decreased of 39%, whereas that of "Costoluto Genovese"/"Natalia" of 11%, compared to control plants. Proteomic results showed a higher representation of proteins associated with pathogen infection in the tolerant rootstock, compared to the sensitive one, meaning a direct involvement of plant defence mechanisms in the tomato response to the pathogen challenge.

Distinct carbohydrate and lipid-based molecular patterns within lipopolysaccharides from Burkholderia cepacia contribute to defense-associated differential gene expression in Arabidopsis thaliana

Lipopolysaccharides are structural components within the cell walls of Gram-negative bacteria. The LPSs as microbe-associated molecular pattern (MAMP) molecules can trigger defense-related responses involved in MAMP-triggered immunity and basal resistance in plants, presumably from an initial perception event. LPS from Burkholderia cepacia as well as two fragments, the glycolipid, lipid A and the polysaccharide (OPS-core) chain, were used to treat Arabidopsis thaliana seedlings to evaluate the eliciting activities of the individual LPS sub-domains by means of Annealing Control Primer-based Differential Display transcript profiling. Genes found to be up-regulated encode for proteins involved in signal perception and transduction, transcriptional regulation and defense - and stress responses. Furthermore, genes encoding proteins involved in chaperoning, secretion, protein-protein interactions and protein degradation were differentially expressed. It is concluded that intact LPS, as well as the two sub-components, induced the expression of a broad range of genes associated with perception and defense as well as metabolic reprogramming of cellular activities in support of immunity and basal resistance. Whilst the lipid A and OPS moieties were able to up-regulate sub-sets of defense-associated genes over the same spectrum of categories as intact LPS, the up-regulation observed with intact LPS was the more comprehensive, suggesting that the lipid A and glycan molecular patterns of the molecule act as partial agonists, but that the intact LPS structure is required for full agonist activity.

Analysis of cotton (Gossypium hirsutum) root proteomes during a compatible interaction with the black root rot fungus Thielaviopsis basicola

A proteomic approach was used to uncover the inducible molecular defense mechanism of cotton root occurring during the compatible interaction with Thielaviopsis basicola. Microscopic observation of cotton root inoculated with a suspension of conidia showed that this necrotrophic hemibiotroph fungus interacts with the plant and completes its life cycle in our experimental system. 2-DE analysis of root extracts taken after 1, 3, 5, and 7 days postinoculation and cluster analysis of the protein expression levels showed four major profiles (constant, upregulated, one slightly downregulated, and one dramatically downregulated). Spots significantly (p<0.05) upregulated were analyzed by LC-MS/MS and identified using MASCOT MS/MS ion search software and associated databases. These proteins included defense and stress related proteins, such as pathogenesis-related proteins and proteins likely to be involved in the oxidative burst, sugar, and nitrogen metabolism as well as amino acid and isoprenoid synthesis. While many of the identified proteins are common components of the defense response of most plants, a proteasome subunit and a protein reported to be induced only in cotton root following Meloidogyne incognita infection were also identified.

Early gene expression changes induced by the bacterial superantigen staphylococcal enterotoxin B and its modulation by a proteasome inhibitor

Toxic shock syndrome (TSS) is an acute, serious systemic illness caused by bacterial superantigens. Nonavailability of a suitable animal model until recently has hampered an in-depth understanding of the pathogenesis of TSS. In the current study, we characterized the early molecular events underlying TSS using our HLA-DR3 transgenic mouse model. Gene expression profiling using DNA microarrays identified a rapid and significant upregulation of several pro- as well as anti-inflammatory mediators, many of which have never been previously described in TSS. In vivo administration of staphylococcal enterotoxin B (SEB) led to an increase in the expression of Th0- (IL-2, 240-fold); Th1- (IFN-gamma, 360-fold; IL-12, 8-fold); Th2- (IL-4, 53-fold; IL-5, 4-fold) as well as Th17-type cytokines (IL-21, 19-fold; IL-17, 5-fold). The immunoregulatory cytokines (IL-6, 700-fold; IL-10, 18-fold); CC chemokines (such as CCL 2, 11, 3, 24, 17, 12, 7), CXC chemokines (such as CXCL 1, 2, 5, 11, 10, 19); and several proteases (matrix metalloproteinases 13, 8, 3, and 9) were also upregulated. Serum levels of several of these cytokines/chemokines were also significantly elevated. Pathway analyses revealed significant modulation in a variety of biochemical and cellular functions, providing molecular insights into the pathogenesis of TSS. Administration of bortezomib, a clinically approved proteasome inhibitor capable of blocking NF-kappaB pathway, was able to significantly modulate the expression of a variety of genes induced by SEB. Thus, our study showed that TSS is a complex process and emphasized the potential of use of bortezomib in the therapy of superantigen-induced TSS.

Overexpression of OgPAE1 from wild rice confers fungal resistance against Botrytis cinerea

A full-length cDNA of the OgPAE1 gene encoding the alpha5 subunit of the 20S proteasome was isolated from wild rice (Oryza grandiglumis) treated by wounding or with a fungal elicitor. The deduced amino acid sequence of OgPAE1 comprises 237 amino acids (25.99 kDa), and shows 94.5% homology with Arabidopsis thaliana AtPAE1. Expression of OgPAE1 is regulated by defense-related signaling chemicals such as cantharidin, endothall and jasmonic acid. Overexpression of OgPAE1 in A. thaliana leads to resistance to the fungal pathogen Botrytis cinerea by lowering disease rate and size of necrotic lesions, and by less penetration and colonization of fungal hyphae. The results indicate that the 20S proteasome from wild rice is involved in the B. cinerea defense pathway via an as yet undetermined mechanism.

Structure, function and regulation of plant proteasomes

Proteasomes are large multisubunit, multicatalytic proteases responsible for most of the cytosolic and nuclear protein degradation, and their structure and functions are conserved in eukaryotes. Proteasomes were originally identified as the proteolytic module of the ubiquitin-dependent proteolysis pathway. Today we know that proteasomes also mediate ubiquitin-independent proteolysis, that they have RNAse activity, and play a non-proteolytic role in transcriptional regulation. Here we present an overview of the current knowledge of proteasome function and regulation in plants and highlight the role of proteasome-dependent protein degradation in the control of plant development and responses to the environment.

Trifluralin herbicide-induced resistance of melon to fusarium wilt involves expression of stress- and defence-related genes

SUMMARY To identify genes involved in trifluralin herbicide-induced resistance of melon to Fusarium oxysporum f. sp. melonis, suppression subtractive hybridization (SSH) and cDNA-amplified fragment-length polymorphism (cDNA-AFLP) were used. A total of 123 clones-60 of which have never been isolated from melon-were isolated, sequenced and annotated. A significant proportion (35%) of the total 123 clones exhibited similarity to genes that have been formerly described as stress- or defence-related. Thirty-two selected clones were subjected to a detailed expression analysis, one-third of which were found to be up-regulated in response to trifluralin treatment and/or fusarium inoculation. The putative roles of seven of these clones in stress are discussed. Furthermore, the expression of four stress-related and up-regulated genes was enhanced when the plants were subjected to salinity stress, suggesting that trifluralin induces a general stress response which protects the plant against fusarium wilt.

The LeATL6-associated ubiquitin/proteasome system may contribute to fungal elicitor-activated defense response via the jasmonic acid-dependent signaling pathway in tomato

The expression of LeATL6, an ortholog of Arabidopsis ATL6 that encodes a RING-H2 finger protein, was induced in tomato roots treated with a cell wall protein fraction (CWP) elicitor of the biocontrol agent Pythium oligandrum. The LeATL6 protein was expressed as a fusion protein with a maltose-binding protein (MBP) in Escherichia coli, and it catalyzed the transfer of ubiquitin to the MBP moiety on incubation with ubiquitin, the ubiquitin-activating enzyme E1, and the ubiquitin-conjugating enzyme E2; this indicated that LeATL6 represents ubiquitin ligase E3. LeATL6 expression also was induced by elicitor treatment of jail-1 mutant tomato cells in which the jasmonic acid (JA)-mediated signaling pathway was impaired; however, JA-dependent expression of the basic PR-6 and TPI-1 genes that encode proteinase inhibitor II and I, respectively, was not induced in elicitor-treated jail-1 mutants. Furthermore, transient overexpression of LeATL6 under the control of the Cauliflower mosaic virus 35S promoter induced the basic PR6 and TPI-1 expression in wild tomato but not in the jail-1 mutant. In contrast, LeATL6 overexpression did not activate salicylic acid-responsive acidic PR-1 and PR-2 promoters in wild tomato. These results indicated that elicitor-responsive LeATL6 probably regulates JA-dependent basic PR6 and TPI-1 gene expression in tomato. The LeATL6-associated ubiquitin/proteasome system may contribute to elicitor-activated defense responses via a JA-dependent signaling pathway in plants.

Molecular cloning and characterization of a rice blast-inducible RING-H2 type zinc finger gene

A novel blast-inducible RING-H2 type zinc finger protein gene OsRING-1 was cloned from rice by cDNA library screening. OsRING-1 is 1670 bp in length and encodes a 46.6 kDa basic protein with two transmembrane (TM) domains, a basic domain (BD), a conserved domain (CD), a RING finger domain and a serine rich (S-rich) domain. By database search, OsRING-1 was mapped on chromosome 2 and clustered together with other six zinc finger genes. The promoter sequence analysis of OsRING-1 gene revealed that some ABA, GA, ethylene, wound, drought, heat stress and pathogen infection responsive elements were found within the OsRING-1 promoter region. Northern analysis showed that OsRING-1 was induced in different degree by pathogen infections, SA, ABA, JA and ethephon (ET) treatments. Tissue expression analysis showed that OsRING-1 was constitutively strongly expressed in roots, but faintly in stems, leaves and sheaths. Taken together, OsRING-1, as a novel C3H2C3-type zinc finger protein involved in many stress responses in rice might plays a role as a transcription regulator in plant stress response signal transduction pathways.

Differential regulation of TGA transcription factors by post-transcriptional control

Transcription factors often belong to multigene families and their individual contribution in a particular regulatory network remains difficult to assess. We show here that specific members from a family of conserved Arabidopsis bZIP transcription factors, the TGA proteins, are regulated in their protein stability by developmental stage-specific proteolysis. Using GFP fusions of three different Arabidopsis TGA factors that represent members of distinct subclasses of the TGA factor family, we demonstrate that two of these TGA proteins are specifically targeted for proteolysis in mature leaf cells. Using a supershift gel mobility assay, we found evidence for similar regulation of the cognate proteins as compared to the GFP fusion proteins expressed under the cauliflower mosaic virus (CaMV) 35S promoter. Using various inhibitors, we showed that the expression of at least one of these three TGA factors could be stabilized by inhibition of proteasome-mediated proteolysis. This study indicates that TGA transcription factors may be regulated by distinct pathways of targeted proteolysis that can serve to modulate the contribution of specific members of a multigene family in complex regulatory pathways.

EL5, a rice N-acetylchitooligosaccharide elicitor-responsive RING-H2 finger protein, is a ubiquitin ligase which functions in vitro in co-operation with an elicitor-responsive ubiquitin-conjugating enzyme, OsUBC5b

EL5, a rice gene responsive to N-acetylchitooligosaccharide elicitor, encodes a RING-H2 finger protein with structural features common to the plant-specific ATL family. We show that the fusion protein of EL5 with maltose binding protein (MBP) was polyubiquitinated by incubation with ubiquitin, ubiquitin-activating enzyme (E1), and the Ubc4/5 subfamily of the ubiquitin-conjugating enzyme (E2). EL5 possesses the activity to catalyse the transfer of ubiquitin to the MBP moiety, and the RING-H2 finger motif of EL5 is necessary for this activity. Thus, we concluded that EL5 represents a ubiquitin ligase (E3). We also show that two rice E2s (OsUBC5a, OsUBC5b) of the Ubc4/5 subfamily function as E2 which catalyses EL5-mediated ubiquitination, and OsUBC5b was induced by elicitor, as well as EL5. These results strongly suggest that EL5 and OsUBC5b have roles in plant defense response through the turnover of protein(s) via the ubiquitin/proteasome system.

Cryptogein affects expression of alpha3, alpha6 and beta1 20S proteasome subunits encoding genes in tobacco

Twelve alpha and beta 20S proteasome subunits cDNAs showing 70-82% identity with the corresponding genes in Arabidopsis or rice, and features of eukaryotic proteasome subunits were cloned in tobacco. Only beta1-tcI 7, alpha3 and alpha6, 20S proteasome subunits encoding genes were up-regulated by cryptogein, a proteinaceous elicitor of plant defence reactions. These results led to the hypothesis that the activation of beta1-tcI 7, alpha3 and alpha6 could induce a specific proteolysis involved in the hypersensitive response and systemic acquired resistance monitored by cryptogein.

Hydrogen peroxide induces programmed cell death features in cultured tobacco BY-2 cells, in a dose-dependent manner

Active oxygen species (AOS), especially hydrogen peroxide, play a critical role in the defence of plants against invading pathogens and in the hypersensitive response (HR). This is characterized by the induction of a massive production of AOS and the rapid appearance of necrotic lesions is considered as a programmed cell death (PCD) process during which a limited number of cells die at the site of infection. This work was aimed at investigating the mode of cell death observed in cultures of BY-2 tobacco cells exposed to H(2)O(2). It was shown that H(2)O(2) is able to induce various morphological cell death features in cultured tobacco BY-2 cells. The hallmarks of cell death observed with fluorescent and electron microscopy differed greatly with the amount of H(2)O(2) added to the cell culture. The appearance of nuclear fragmentation similar to 'apoptotic bodies' associated with a fragmentation of the nuclear DNA into small fragments appear for almost 18% of the cells treated with 12.5 mM H(2)O(2). The early stages of the induction of this PCD process consisted in cell shrinkage and chromatin condensation at the periphery of the nucleus. Above 50 mM, H(2)O(2) induces high necrotic cell death. These data suggest that H(2)O(2)-induced cell damage is associated with the induction of various cell death processes that could be involved differently in plant defence reactions.

Ubiquitin- and proteasome-dependent proteolysis in plants

In recent years it has become obvious that protein degradation is an important catabolic process during development in plants and animals. One very conserved degradative system is the ubiquitin- and proteasome-dependent proteolytic pathway, which is found in all eukaryotes from yeast to mammals and plants. The pathway consists of two parts, one in which chains of ubiquitin are conjugated to substrate proteins, and one in which these substrate proteins are either degraded by the 26S proteasome or are de-ubiquitinated. The ubiquitin- and proteasome-dependent pathway degrades a wide range of proteins in the nucleus and cytoplasm. It is highly specific, but controls a large number of cellular events due to the diversity in the conjugating enzymes. This pathway is important for removal of abnormal/damaged proteins that have had their recognition sites exposed as well as for control of specific transcription factors and cell cycle regulators. In plants, ubiquitin- and proteasome-dependent proteolysis is known to be involved in regulation of the cell cycle and transcription factors as well as endoplasmic reticulum-associated protein degradation, stress response and developmental processes, such as xylogenesis and senescence.

Transcriptionally and post-transcriptionally regulated response of 13 calmodulin genes to tobacco mosaic virus-induced cell death and wounding in tobacco plant

We isolated 13 tobacco calmodulin (CaM) genes, NtCaM1-13, and analyzed their expression profile in response to pathogen infection and wounding using specific DNA probes for individual CaM genes and specific antibodies for CaM proteins in groups I (NtCaM1/2), II (NtCaM3/4/5/6/7/8/11/12 and 9/10) and III (NtCaM13), respectively. Synchronous cell death in tobacco mosaic virus (TMV)-infected N-gene-containing tobacco leaves accompanied a predominant accumulation of NtCaM1, 2 and 13 transcripts and NtCaM13-type protein, which is a possible ortholog of soybean defense-involved CaM (SCaM-4), preceding induction of PR-1 and PR-3 defense genes. Accumulation of NtCaM1, 2, 3 and 4 transcripts was induced within 30 min after wounding and NtCaM1-type protein accumulated transiently after wounding. NtCaM13-type protein, which was found at a low level in healthy leaves, decreased instantly after wounding. The treatment with a proteasome inhibitor, lactacystin, enhanced wound-induced accumulation of NtCaM1-type protein and inhibited wound-induced decrease of NtCaM13-type protein, suggesting that proteasome activity is involved in the degradation of these CaMs. Thus, our results indicate that levels of individual CaM proteins are differentially regulated both transcriptionally and post-transcriptionally in tobacco plants that are exposed to stresses such as pathogen-induced hypersensitive cell death and wounding.

Inhibition of proteasome activity strongly affects kiwifruit pollen germination. Involvement of the ubiquitin/proteasome pathway as a major regulator

The 26S proteasome is a multicatalytic complex that acts as primary protease of the ubiquitin-mediated proteolytic pathway in eukaryotes. We provide here the first evidence that the proteasome plays a key role in regulating pollen tube growth. Immunoblotting experiments revealed the presence of high levels of free ubiquitin and ubiquitin conjugates in rehydrated and germinating pollen of kiwifruit [Actinidia deliciosa var. deliciosa (A. Chev) C. F. Liang et A. R. Ferguson]. Proteasome activity, assayed fluorometrically, accompanied the progression of germination. Specific inhibitors of proteasome function such as benzyloxycarbonyl-leucinyl-leucinyl-leucinal (MG-132), clasto-lactacystin beta-lactone, and epoxomicin significantly decreased tube growth or altered tube morphology. High-molecular mass, ubiquitinated proteins accumulated in MG-132- and beta-lactone-treated pollen, indicating that proteasome function was effectively impaired. The inhibitors were also able to decrease in vitro proteasome activity in pollen extracts. Because MG-132 can inhibit calpains, as well as the proteasome, trans-epoxy succinyl-L-leucylamido-(4-guanidino) butane (E-64), an inhibitor of cysteine proteases, was investigated. Some reduction in tube growth rate was observed, but only at 80 microM E-64, and no abnormal tubes were produced. Furthermore, no inhibition of tube growth was observed when another inhibitor of cysteine proteases, leupeptin, or inhibitors of serine and aspartic proteases (phenylmethylsulfonyl fluoride and pepstatin) were used. Our results indicate that protein turnover during tube organization and elongation in kiwifruit pollen is important, and our results also implicate the ubiquitin/26S proteasome as the major proteolytic pathway involved.

beta-Aminobutyric acid-induced protection of Arabidopsis against the necrotrophic fungus Botrytis cinerea

The non-protein amino acid beta-aminobutyric acid (BABA) protects numerous plants against various pathogens. Protection of Arabidopsis plants against virulent pathogens involves the potentiation of pathogen-specific defense responses. To extend the analysis of the mode of action of BABA to necrotrophs we evaluated the effect of this chemical on Arabidopsis plants infected with the gray mold fungus Botrytis cinerea. BABA-treated Arabidopsis were found to be less sensitive to two different strains of this pathogen. BABA protected mutants defective in the jasmonate and ethylene pathways, but was inactive in plants impaired in the systemic acquired resistance transduction pathway. Treatments with benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester, a functional analog of salicylic acid (SA), also markedly reduced the level of infection. Moreover, BABA potentiated mRNA accumulation of the SA-associated PR-1, but not the jasmonate/ethylene-dependent PDF1.2 gene. Thus, besides jasmonate/ethylene-dependent defense responses, SA-dependent signaling also contributes to restrict B. cinerea infection in Arabidopsis. Our results also suggest that SA-dependent signaling is down-regulated after infection by B. cinerea. The observed up-regulation of the PDF1.2 gene in mutants defective in the SA-dependent signaling pathway points to a cross-talk between SA- and jasmonate/ethylene-dependent signaling pathways during pathogen ingress.

Isolation and analysis of expression mechanisms of a rice gene, EL5, which shows structural similarity to ATL family from Arabidopsis, in response to N-acetylchitooligosaccharide elicitor

Two rice cDNAs, EL5 and RRF1, were isolated and characterized. EL5 was responsive to N-acetylchitooligosaccharide, a biotic elicitor active in suspension-cultured rice cells. The structural specificity of the elicitor required for the expression of EL5 was consistent with other defense reactions observed in the experimental system, indicating that the elicitor signal to EL5 is transmitted through a single class of receptor-mediated recognition events. However, the intracellular signaling pathway to EL5 was distinct from those to other elicitor-responsive genes. Sequence analysis and alignment showed that a genomic sequence stored in rice genome databases in addition to EL5 and RRF1 belongs to the ATL family of RING-H2 finger motif proteins first isolated from Arabidopsis.

Gene responses in bean leaves induced by herbivory and by herbivore-induced volatiles

Plant-plant interactions via herbivory-induced leaf volatiles could result in the induction of defense responses against aggressive biotic agents in plants. In this study, cDNA microarray technology showed comprehensive gene activation in lima bean leaves that were exposed to volatiles released from the neighboring leaves infested with spider mites. The infestation with spider mites and the herbivory-induced volatiles enhanced 97 and 227 gene spots on the microarray tip printed with 2032 lima bean cDNA, respectively. These genes are related to such broad functions as responses to pathogenesis, wounding, hormones, ethylene biosynthesis, flavonoid biosynthesis, (post) transcriptional modifications, translations, chaperones, secondary signaling messengers, membrane transports, protein/peptide degradations, and photosynthesis. We therefore conclude that herbivorous damage and herbivory-induced volatiles elicit comprehensive and drastic changes of metabolisms in leaves.

Protein degradation in signaling

Recent studies have linked proteolysis by the ubiquitin/proteasome pathway to a variety of signaling pathways in higher plants. These links were uncovered by characterization of mutants altered in signaling or by targeted disruption of components of the proteolytic pathway. Significant advances have recently revealed connections between proteolysis and hormone responses, light perception, environmental adaptation, and floral development.