A major stylar matrix polypeptide (sp41) is a member of the pathogenesis-related proteins superclass

Pectate lyase-like lubricates the male gametophyte's path toward its mating partner

The pollen tube is an extension of the male gametophyte in plants and mediates sexual reproduction by delivering the sperm cells to the female gametophyte. To accomplish this task, the elongating pollen tube must break through the thick wall of the pollen grain and penetrate multiple pistillar tissues. Both processes require the loosening of cell wall material-that of the pollen intine and that of the apoplast of the transmitting tract. The enzymatic toolbox for these cell wall modifying processes employed by the invading male gametophyte is elusive. We investigated the role of the pectin-digesting pectate lyase-like (PLL) by combining mutant analysis with microscopy observations, fluorescence recovery after photo-bleaching experiments, and immuno-detection. We show that in Arabidopsis (Arabidopsis thaliana), PLLs are required for intine loosening during the first steps of pollen tube germination. We provide evidence that during pollen tube elongation, PLLs are released by the pollen tube into the extracellular space, suggesting that they may be employed to soften the apoplast of the transmitting tissue. The synergistic enzymatic action of PLLs in the pollen grain, the pollen tube, and the transmitting track contribute to an effective fertilization process.

A loss-of-function mutant allele of a glycosyl hydrolase gene has been co-opted for seed weight control during soybean domestication

The resultant DNA from loss-of-function mutation can be recruited in biological evolution and development. Here, we present such a rare and potential case of "to gain by loss" as a neomorphic mutation during soybean domestication for increasing seed weight. Using a population derived from a chromosome segment substitution line of Glycine max (SN14) and Glycine soja (ZYD06), a quantitative trait locus (QTL) of 100-seed weight (qHSW) was mapped on chromosome 11, corresponding to a truncated β-1, 3-glucosidase (βGlu) gene. The novel gene hsw results from a 14-bp deletion, causing a frameshift mutation and a premature stop codon in the βGlu. In contrast to HSW, the hsw completely lost βGlu activity and function but acquired a novel function to promote cell expansion, thus increasing seed weight. Overexpressing hsw instead of HSW produced large soybean seeds, and surprisingly, truncating hsw via gene editing further increased the seed size. We further found that the core 21-aa peptide of hsw and its variants acted as a promoter of seed size. Transcriptomic variation in these transgenic soybean lines substantiated the integration hsw into cell and seed size control. Moreover, the hsw allele underwent selection and expansion during soybean domestication and improvement. Our work cloned a likely domesticated QTL controlling soybean seed weight, revealed a novel genetic variation and mechanism in soybean domestication, and provided new insight into crop domestication and breeding, and plant evolution.

A novel β-1,3-glucanase Gns6 from rice possesses antifungal activity against Magnaporthe oryzae

As members of the pathogenesis-related protein (PR)-2 family, β-1,3-glucanases play pivotal roles in plant defense. Previous study showed that the rice genome contains 16 genes encoding putative β-1,3-glucanases, and the β-1,3-glucanases in subfamily A were deduced to be involved in plant defense. However, there was limited direct evidence. In this study, the expression of rice β-1,3-glucanases Gns2-Gns6 belonging to subfamily A in rice plant infection with Magnaporthe oryzae was investigated, and the enhanced expression of Gns6 during infection confirmed its crucial role in the defense of rice seedlings. Enzymological characterization revealed that Gns6 preferentially hydrolyzed laminarin, pachymaran, and yeast glucan. The β-1,3; 1,6-glucanase Gns6 exhibited a specific activity of 1.2 U/mg with laminarin as the substrate. In addition, Gns6 could hydrolyze laminarin via an endo-type mechanism, yielding a series of oligosaccharides with various degrees of polymerization that are known immune elicitors in plants. Moreover, Gns6 exhibited a significant inhibitory effect against the formation of the germ tubes and appressoria, with potential applications in plant protection. Taken together, this study shows that Gns6 is an essential effector in the defensive response of rice against pathogenic fungi.

Laminarans and 1,3-β-D-glucanases

The laminarans are biologically active water-soluble polysaccharide (1,3;1,6-β-D-glucans) of brown algae. These polysaccharides are an attractive object for research due to its relatively simple structure, low toxicity, and various biological effects. 1,3-β-D-glucanases are an effective tool for studying the structure of laminarans, and can also be used to obtain new biologically active derivatives. This review is to outline what is currently known about laminarans and enzymes that catalyze of their transformation. We focused on information about sources, structure and properties of laminarans and 1,3-β-D-glucanases, methods of obtaining and structural elucidation of laminarans, and biological activity of laminarans and products of their enzymatic transformation. It has an increased focus on the immunomodulating and anticancer activity of laminarans and their derivatives.

High Constitutive Overexpression of Glycosyl Hydrolase Family 17 Delays Floral Transition by Enhancing FLC Expression in Transgenic Arabidopsis

Vitis vinifera glycosyl hydrolase family 17 (VvGHF17) is a grape apoplasmic β-1,3-glucanase, which belongs to glycosyl hydrolase family 17 in grapevines. β-1,3-glucanase is not only involved in plant defense response but also has various physiological functions in plants. Although VvGHF17 expression is negatively related to the length of inflorescence in grapevines, the physiological functions of VvGHF17 are still uncertain. To clarify the physiological functions of VvGHF17, we conducted a phenotypic analysis of VvGHF17-overexpressing Arabidopsis plants. VvGHF17-overexpressing Arabidopsis plants showed short inflorescence, similar to grapevines. These results suggested that VvGHF17 might negatively regulate the length of inflorescence in plants. VvGHF17 expression induced a delay of floral transition in Arabidopsis plants. The expression level of FLOWERING LOCUS C (FLC), known as a floral repressor gene, in inflorescence meristem of transgenic plants were increased by approximately 10-fold as compared with wild plants. These results suggest that VvGHF17 induces a delay of floral transition by enhancing FLC expression and concomitantly decreases the length of plant inflorescence.

ZmGns, a maize class I β-1,3-glucanase, is induced by biotic stresses and possesses strong antimicrobial activity

Plant β-1,3-glucanases are members of the pathogenesis-related protein 2 (PR-2) family, which is one of the 17 PR protein families and plays important roles in biotic and abiotic stress responses. One of the differentially expressed proteins (spot 842) identified in a recent proteomic comparison between five pairs of closely related maize (Zea mays L.) lines differing in aflatoxin resistance was further investigated in the present study. Here, the corresponding cDNA was cloned from maize and designated as ZmGns. ZmGns encodes a protein of 338 amino acids containing a potential signal peptide. The expression of ZmGns was detectible in all tissues studied with the highest level in silks. ZmGns was significantly induced by biotic stresses including three bacteria and the fungus Aspergillus flavus. ZmGns was also induced by most abiotic stresses tested and growth hormones including salicylic acid. In vivo, ZmGns showed a significant inhibitory activity against the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and fungal pathogen Botrytis cinerea when it overexpressed in Arabidopsis. Its high level of expression in the silk tissue and its induced expression by phytohormone treatment, as well as by bacterial and fungal infections, suggest it plays a complex role in maize growth, development, and defense.

The transmitting tissue of Nicotiana tabacum is not essential to pollen tube growth, and its ablation can reverse prezygotic interspecific barriers

The Nicotiana tabacum transmitting tissue is a highly specialized file of metabolically active cells that is the pathway for pollen tubes from the stigma to the ovules where fertilization occurs. It is thought to be essential to pollen tube growth because of the nutrients and guidance it provides to the pollen tubes. It also regulates gametophytic self-incompatibility in the style. To test the function of the transmitting tissue in pollen tube growth and to determine its role in regulating prezygotic interspecific incompatibility, genetic ablation was used to eliminate the mature transmitting tissue, producing a hollow style. Despite the absence of the mature transmitting tissue and greatly reduced transmitting-tissue-specific gene expression, self-pollen tubes had growth to the end of the style. Pollen tubes grew at a slower rate in the transmitting-tissue-ablated line during the first 24 h post-pollination. However, pollen tubes grew to a similar length 40 h post-pollination with and without a transmitting tissue. Ablation of the N. tabacum transmitting tissue significantly altered interspecific pollen tube growth. These results implicate the N. tabacum transmitting tissue in facilitating or inhibiting interspecific pollen tube growth in a species-dependent manner and in controlling prezygotic reproductive barriers.

Glucan-rich diet is digested and taken up by the carnivorous sundew (Drosera rotundifolia L.): implication for a novel role of plant β-1,3-glucanases

Carnivory in plants evolved as an adaptation strategy to nutrient-poor environments. Thanks to specialized traps, carnivorous plants can gain nutrients from various heterotrophic sources such as small insects. Digestion in traps requires a coordinated action of several hydrolytic enzymes that break down complex substances into simple absorbable nutrients. Among these, several pathogenesis-related proteins including β-1,3-glucanases have previously been identified in digestive fluid of some carnivorous species. Here we show that a single acidic endo-β-1,3-glucanase of ~50 kDa is present in the digestive fluid of the flypaper-trapped sundew (Drosera rotundifolia L.). The enzyme is inducible with a complex plant β-glucan laminarin from which it releases simple saccharides when supplied to leaves as a substrate. Moreover, thin-layer chromatography of digestive exudates showed that the simplest degradation products (especially glucose) are taken up by the leaves. These results for the first time point on involvement of β-1,3-glucanases in digestion of carnivorous plants and demonstrate the uptake of saccharide-based compounds by traps. Such a strategy could enable the plant to utilize other types of nutritional sources e.g., pollen grains, fungal spores or detritus from environment. Possible multiple roles of β-1,3-glucanases in the digestive fluid of carnivorous sundew are also discussed.

Fibres from flax overproducing β-1,3-glucanase show increased accumulation of pectin and phenolics and thus higher antioxidant capacity

BACKGROUND

Recently, in order to improve the resistance of flax plants to pathogen infection, transgenic flax that overproduces β-1,3-glucanase was created. β-1,3-glucanase is a PR protein that hydrolyses the β-glucans, which are a major component of the cell wall in many groups of fungi. For this study, we used fourth-generation field-cultivated plants of the Fusarium -resistant transgenic line B14 to evaluate how overexpression of the β-1,3-glucanase gene influences the quantity, quality and composition of flax fibres, which are the main product obtained from flax straw.

RESULTS

Overproduction of β-1,3-glucanase did not affect the quantity of the fibre obtained from the flax straw and did not significantly alter the essential mechanical characteristics of the retted fibres. However, changes in the contents of the major components of the cell wall (cellulose, hemicellulose, pectin and lignin) were revealed. Overexpression of the β-1,3-glucanase gene resulted in higher cellulose, hemicellulose and pectin contents and a lower lignin content in the fibres. Increases in the uronic acid content in particular fractions (with the exception of the 1 M KOH-soluble fraction of hemicelluloses) and changes in the sugar composition of the cell wall were detected in the fibres of the transgenic flax when compared to the contents for the control plants. The callose content was lower in the fibres of the transgenic flax. Additionally, the analysis of phenolic compound contents in five fractions of the cell wall revealed important changes, which were reflected in the antioxidant potential of these fractions.

CONCLUSION

Overexpression of the β-1,3-glucanase gene has a significant influence on the biochemical composition of flax fibres. The constitutive overproduction of β-1,3-glucanase causes a decrease in the callose content, and the resulting excess glucose serves as a substrate for the production of other polysaccharides. The monosaccharide excess redirects the phenolic compounds to bind with polysaccharides instead of to partake in lignin synthesis. The mechanical properties of the transgenic fibres are strengthened by their improved biochemical composition, and the increased antioxidant potential of the fibres supports the potential use of transgenic flax fibres for biomedical applications.

Biology of callose (β-1,3-glucan) turnover at plasmodesmata

The turnover of callose (β-1,3-glucan) within cell walls is an essential process affecting many developmental, physiological and stress related processes in plants. The deposition and degradation of callose at the neck region of plasmodesmata (Pd) is one of the cellular control mechanisms regulating Pd permeability during both abiotic and biotic stresses. Callose accumulation at Pd is controlled by callose synthases (CalS; EC 2.4.1.34), endogenous enzymes mediating callose synthesis, and by β-1,3-glucanases (BG; EC 3.2.1.39), hydrolytic enzymes which specifically degrade callose. Transcriptional and posttranslational regulation of some CalSs and BGs are strongly controlled by stress signaling, such as that resulting from pathogen invasion. We review the role of Pd-associated callose in the regulation of intercellular communication during developmental, physiological, and stress response processes. Special emphasis is placed on the involvement of Pd-callose in viral pathogenicity. Callose accumulation at Pd restricts virus movement in both compatible and incompatible interactions, while its degradation promotes pathogen spread. Hence, studies on mechanisms of callose turnover at Pd during viral cell-to-cell spread are of importance for our understanding of host mechanisms exploited by viruses in order to successfully spread within the infected plant.

Molecular characterization and differential expression of beta-1,3-glucanase during ripening in banana fruit in response to ethylene, auxin, ABA, wounding, cold and light-dark cycles

beta-1,3-Glucanases (E.C. 3.2.1.39) are widely distributed enzyme among bacteria, fungi, and higher plants. Analyses of accumulation levels of beta-1,3-glucanase protein in various tissues in banana have clearly indicated abundance of beta-1,3-glucanase protein accumulation in ripe pulp tissue. After cloning of beta-1,3-glucanase from banana pulp (cultivar Cavendish), we have carried out an in silico analysis to investigate the sequential, structural, and phylogenetic characteristics of the putative banana beta-1,3-glucanase protein. As like other ripening specific genes, beta-1,3-glucanase is regulated in response to a wide variety of factors. Therefore, we have analyzed the transcript accumulation pattern and protein levels of beta-1,3-glucanase in response to ethylene, auxin, ABA, wounding and, low temperature in preclimacteric banana fruit. Expression profile analyses have indicated that whereas exogenous application of ethylene strongly stimulated beta-1,3-glucanase transcript accumulation, ABA partially induced the expression of the gene. On the other hand, wound treatment did not induce beta-1,3-glucanase expression. Conversely, auxin and cold treatment negatively regulated beta-1,3-glucanase gene expression and thus inhibited glucanase activity. In addition, beta-1,3-glucanase transcript level was markedly decreased by constant exposure to white light. Protein level and enzymatic activity of beta-1,3-glucanase were substantially increased with considerable decrease in fruit firmness by ethylene treatment and reduced exposure to white light conditions as compared with other treatments. Together, the overall study of beta-1,3-glucanase expression pattern, glucanase activity, and changes in fruit firmness during ripening in various conditions suggest the possible physiological function of beta-1,3-glucanase in fruit pulp softening.

Characterization of cultivar differences in beta-1,3 glucanase gene expression, glucanase activity and fruit pulp softening rates during fruit ripening in three naturally occurring banana cultivars

beta-1,3 glucanase (E.C.3.2.1.39) is the key enzyme involved in the hydrolytic cleavage of 1,3 beta-D glucosidic linkages in beta-1,3 glucans. This work describes a comparative analysis of expression patterns of beta-1,3 glucanase gene in relation to changes in fruit pulp softening rates in three banana cultivars, Rasthali (AAB), Kanthali (AB), and Monthan (ABB). Analysis of transcript and protein levels of beta-1,3 glucanase gene during ripening revealed differential timing in expression of the gene which correlated well with the variation in enzymatic activity of glucanase and fruit pulp softening rates in the three cultivars. Exogenously applied ethylene strongly induced beta-1,3 glucanase expression during the early ripening days in Rasthali, while the expression of the gene was marginally stimulated following ethylene treatment in preclimacteric Kanthali fruit. Conversely, in Monthan, beta-1,3 glucanase expression was very low throughout the ripening stages, and ethylene treatment did not induce the expression of the gene in this cultivar. Analysis of glucanase activity using protein extracts from unripe and ripe fruit of Monthan with crude cell wall polysaccharide fractions (used as substrate) indicated that the natural substrate for glucanase remained almost unutilized in this cultivar due to low in vivo glucanase activity. Furthermore, the recombinant beta-1,3 glucanase protein, overexpressed in E. coli, showed requirement for substrates with contiguous beta-1,3 linkages for optimal activity. Overall, our results provide new information on the expression profile of beta-1,3 glucanase gene in connection with the pattern of changes in fruit firmness at the physiological and molecular levels during ripening in three banana cultivars.

Production of male- and female-sterile plants through reproductive tissue ablation

Male and female sterilities have many useful applications in horticultural crops, including reducing the invasive potential of new ornamentals, elimination of pollen allergens and redirecting resources from seeds to vegetative growth. In this study, we tested a male- and female-sterility (MS; FS) gene construct in Nicotiana tabacum to evaluate its effectiveness and effect on phenotype. Three T1 Nicotiana tabacum lines expressing the MS (p108:barnase) and FS (sp41:barnase) genes (MS/FS lines) and a control Nicotiana tabacum line (WT GUS) were measured for plant height, leaf length and width, corolla length, number of nodes on the main stem and stem diameter. No significant differences were found in these growth measurements between MS/FS lines and WT GUS. No pollen was observed on any of the lines carrying the MS and FS genes, indicating that the male sterility was complete. Seed set was greatly reduced or completely eliminated in plants with the MS and FS genes, after heavy pollinations of mature flowers with WT GUS pollen. However, pollinations of immature flowers resulted in very low seed set. This may be due to the nature of the promoter controlling expression of the FS gene as it had the highest expression levels at anthesis. The combination of male- and female-sterility genes was effective in eliminating seed set in all the lines examined and has direct application for reducing invasiveness of ornamental plants.

Male-fertility genes expressed in male flower buds of Silene latifolia include homologs of anther-specific genes

When the female plant of Silene latifolia is infected with the smut fungus Microbotryum violaceum, its rudimentary stamens develop into anthers which contain fungus teliospores instead of pollen. To identify genes required for maturation of anthers in S. latifolia, we performed a cDNA subtraction approach with healthy male buds and female buds infected with M. violaceum. We isolated five cDNA clones, which were preferentially expressed in healthy male buds during stages associated with a burst in tapetal activity. These five cDNAs are predicted to encode a mandelonitrile lyase protein (SlMDL1), a strictosidine synthase protein (SlSs), a glycosyl hydrolase 17 protein (SlGh17), a proline-rich protein APG precursor (SlAPG), and a chalcone-synthase-like protein (SlChs). All five genes showed expression in both healthy and fungus-infected male buds, but not expressed in either healthy or infected female buds. The first three genes were highly expressed in both tapetum and pollen grains while the last two genes were expressed only inside the tapetum of male flower buds. Phylogenetic analysis results showed that SlChs and SlGh17 belong to anther-specific subgroups of chalcone-synthase-like genes and glycosyl hydrolase 17 family genes, respectively. Our results suggest that the isolated five genes are related to the fertility of the anther leading to the development of fertile pollen. The smut fungus was not able to induce the expression of the five genes in the infected female buds. This raises the possibility that these genes are under the control of master gene(s) on the Y chromosome.

Analysis of the Nicotiana tabacum stigma/style transcriptome reveals gene expression differences between wet and dry stigma species

The success of plant reproduction depends on pollen-pistil interactions occurring at the stigma/style. These interactions vary depending on the stigma type: wet or dry. Tobacco (Nicotiana tabacum) represents a model of wet stigma, and its stigmas/styles express genes to accomplish the appropriate functions. For a large-scale study of gene expression during tobacco pistil development and preparation for pollination, we generated 11,216 high-quality expressed sequence tags (ESTs) from stigmas/styles and created the TOBEST database. These ESTs were assembled in 6,177 clusters, from which 52.1% are pistil transcripts/genes of unknown function. The 21 clusters with the highest number of ESTs (putative higher expression levels) correspond to genes associated with defense mechanisms or pollen-pistil interactions. The database analysis unraveled tobacco sequences homologous to the Arabidopsis (Arabidopsis thaliana) genes involved in specifying pistil identity or determining normal pistil morphology and function. Additionally, 782 independent clusters were examined by macroarray, revealing 46 stigma/style preferentially expressed genes. Real-time reverse transcription-polymerase chain reaction experiments validated the pistil-preferential expression for nine out of 10 genes tested. A search for these 46 genes in the Arabidopsis pistil data sets demonstrated that only 11 sequences, with putative equivalent molecular functions, are expressed in this dry stigma species. The reverse search for the Arabidopsis pistil genes in the TOBEST exposed a partial overlap between these dry and wet stigma transcriptomes. The TOBEST represents the most extensive survey of gene expression in the stigmas/styles of wet stigma plants, and our results indicate that wet and dry stigmas/styles express common as well as distinct genes in preparation for the pollination process.

Low responsiveness of grapevine flowers and berries at fruit set to UV-C irradiation

In grapevine, stimulation of defence responses was evidenced in response to various types of abiotic stresses in both leaves and berries, as revealed by the increasing expression of genes encoding defence-related proteins or the stimulation of their corresponding activities. However, the capability of inflorescences to respond to abiotic stresses has never been investigated. Therefore, plant defence reactions in response to UV-C irradiation were followed in inflorescences and young clusters focusing on both bunchstems (peduncle and pedicels) and developing flowers/berries from separated floral buds stage [Biologische Bundesanstalt, Bundessortenamt and CHemical industry (BBCH) stage 57] to groat-sized berries stage (BBCH 73). For this purpose, the expression of various genes coding for pathogenesis-related (PR) proteins (class I and III chitinases, Chi1b and CH3; beta-1,3-glucanase, GLUC), an enzyme of the phenylpropanoid pathway (phenylalanine ammonia-lyase, PAL), and stilbene synthase (STS) was analysed in parallel with variations of chitinase activity and the accumulation of the phytoalexin resveratrol. Multiple defence responses were induced in bunchstems of both inflorescences and clusters following UV-C treatment. First, expression of genes encoding PR proteins was stimulated and chitinase activity was enhanced. Secondly, PAL and STS expression increased in association with resveratrol accumulation. Amazingly, none of the tested defence processes was induced in grapevine flowers following UV-C exposure, whatever the stage analysed. Similarly, in berries at fruit set, induction of gene expression was weak and neither an increase in chitinase activity nor resveratrol synthesis was noticed. However, in groat-sized berries, responsiveness to UV-C increased, as revealed by the induction of CH3, PAL, and STS expression, together with resveratrol accumulation. The differential responsiveness between bunchstems, flowers, and berries is discussed.

Co-Localization of beta-1,3-Glucanases and Callose During Somatic Embryogenesis in Cichorium

During direct somatic embryogenesis in leaves of Cichorium hybrid clone '474', 38 kDa beta-1,3-glucanases are accumulated in the culture medium of the embryogenic hybrid to a higher level when compared with a non-embryogenic cultivar. In the same time, embryogenic cells were surrounded by a cell wall that was characterized by the presence of callose. This callosic deposition disappeared as embryos grew. Callose consisted of beta-1,3-glucan linkages and so represented a possible substrate for beta-1,3-glucanases. Using immunolocalization experiments, we demonstrated that from the three types of callose deposits observed during the culturing of Cichorium leaf explants, only the callose present in the walls surrounding reactivated cells seemed specifically related to somatic embryogenesis. Moreover, callose and the 38-kDa beta-1,3-glucanases were co-localized dispersed throughout the thick and swelled walls of reactivated cells and embryo cell walls. This suggests that callose and beta-1,3-glucanases are implicated in the process of somatic embryogenesis since they were always detected in or quite near embryogenic and embryo cell. This also suggested that beta-1,3-glucanases could be involved in the degradation of this callose.

A plasmodesmata-associated beta-1,3-glucanase in Arabidopsis

Plasmodesmal conductivity is regulated in part by callose turnover, which is hypothesized to be determined by beta-1,3-glucan synthase versus glucanase activities. A proteomic analysis of an Arabidopsis thaliana plasmodesmata (Pd)-rich fraction identified a beta-1,3-glucanase as present in this fraction. The protein encoded by the putative plasmodesmal associated protein (ppap) gene, termed AtBG_ppap, had previously been found to be a post-translationally modified glycosylphosphatidylinositol (GPI) lipid-anchored protein. When fused to green fluorescent protein (GFP) and expressed in tobacco (Nicotiana tabacum) or Nicotiana benthamiana epidermal cells, this protein displays fluorescence patterns in the endoplasmic reticulum (ER) membrane system, along the cell periphery and in a punctate pattern that co-localizes with aniline blue-stained callose present around the Pd. Plasma membrane localization was verified by co-localization of AtBG_ppap:GFP together with a plasma membrane marker N-[3-triethylammoniumpropyl]-4-[p-diethylaminophenylhexatrienyl] pyridinium dibromide (FM4-64) in plasmolysed cells. In Arabidopsis T-DNA insertion mutants that do not transcribe AtBG_ppap, functional studies showed that GFP cell-to-cell movement between epidermal cells is reduced, and the conductivity coefficient of Pd is lower. Measurements of callose levels around Pd after wounding revealed that callose accumulation in the mutant plants was higher. Taken together, we suggest that AtBG_ppap is a Pd-associated membrane protein involved in plasmodesmal callose degradation, and functions in the gating of Pd.

Isolation and differential expression of β-1,3-glucanase messenger RNAs, SrGLU3 and SrGLU4, following inoculation of Sesbania rostrata

We report here the isolation and characterisation of two new β-1,3-glucanase cDNAs, SrGLU3 and SrGLU4, from a tropical legume Sesbania rostrata Bremek. & Oberm., which form N₂-fixing nodules on the stem after infection by Azorhizobium caulinodans. SrGLU3 was characterised as being grouped in a branch with tobacco class I β-1,3-glucanases, where the isoforms were reported to be induced by either pathogen infection or ethylene treatment. SrGLU4 was characterised as separate from other classes, and we propose this new branch as a new class (Class VI). The SrGLU3 gene was constitutively expressed in normal stem nodules induced by the wild type strain of A. caulinodans (ORS571), and also even in immature stem nodules induced by a mutant (ORS571-C1), which could not form mature stem-nodules. In contrast, the transcript accumulation of SrGLU4 was hardly detectable in immature nodules inoculated by the ORS571-C1 mutant. We suggest that S. rostrata makes use of SrGLU4 to discriminate between symbionts and non-symbionts (mutants) in developing nodules. We propose the SrGLU4 gene as a new nodulin during nodulation.

The rolC gene induces expression of a pathogenesis-related beta-1,3-glucanase in transformed ginseng cells

The Agrobacterium rhizogenes rolC oncogene is capable of stimulating production of secondary metabolites in transformed plant cells that suggest its possible involvement in plant defense reactions. We tested whether the gene could also affect production of pathogenesis-related proteins. Using a well-known group of PR-proteins, such as beta-1,3-glucanases, we observed a 10-fold increase in total beta-1,3-glucanase activity in rolC-transformed Panax ginseng cells compared with normal cells. The increase was due to the production of a salicylic acid-activated beta-1,3-glucanase isoform. We isolated cDNA of the corresponding beta-1,3-glucanase gene (Pg-glu1), which shared 38-60% sequence identity with previously reported sequences of plant beta-1,3-glucanases at the protein level. Levels of Pg-glu1 mRNA transcripts were tightly correlated with expression of the rolC gene. Our data, together with previously reported information, indicate that A. rhizogenes can activate plant defense reactions via expression of T-DNA oncogenes.

In silico insight into two rice chromosomal regions associated with submergence tolerance and resistance to bacterial leaf blight and gall midge

Plants respond to both biotic and abiotic stresses through a common signaling system to provide defense and protection against many adverse environments. Many genes/QTLs governing resistance to both biotic and abiotic stresses have been studied and mapped in rice. Sub1, a major QTL for submergence tolerance is collocated with a gene Gm1 for gall midge resistance on chromosome 9 (Region 1). Likewise a bigger region on chromosome 5 (Region 2) has a minor QTL for submergence tolerance collocated with genes for bacterial blight resistance. Utilizing the rice sequence and annotation data (TIGR) and rice genome annotation project database (RAP-DB), we wanted to know the kinds of genes underlying these two chromosomal regions where genes/QTL governing tolerance to both biotic and abiotic stresses are collocated. We also analyzed the pattern of distribution of these genes across the BAC/PAC clones spanning the region so that candidate genes can be short listed for a functional analysis. Genes known to have a role in submergence tolerance were present in both the regions. Region 1, had a unique transcription factor like trithorax protein, which is a positional candidate gene for submergence tolerance. Pyruvate decarboxylase (PDC) gene for alcohol fermentation and cation transporting ATPase c-terminal domain are likely candidates for submergence QTL in Region 2. Genes such as SKP1 and elicitor induced cytochrome p450 associated with tissue necrosis and insect resistance were found in region 1. Multiple copies of ORFs for signal transduction proteins, transcription factors, genes for systemic acquired resistance, Ubiquitin proteins and pathogen elicitor identification and degrading proteins were located as a cluster in Region 2, where bacterial blight resistance genes mapped. Validation of the data obtained from TIGR with other databases (RAP and KOME) confirmed our findings. The functional role of some of the significant candidate genes needs to be established. Allele/gene specific markers can then be designed for use in MAS thus enhancing durable tolerance/resistance faster.

Comprehensive approach to genes involved in cell wall modifications in Arabidopsis thaliana

The plant cell wall is of supermolecular architecture, and is composed of various types of heterogeneous polymers. A few thousand enzymes and structural proteins are directly involved in the construction processes, and in the functional aspects of the dynamic architecture in Arabidopsis thaliana. Most of these proteins are encoded by multigene families, and most members within each family share significant similarities in structural features, but often exhibit differing expression profiles and physiological functions. Thus, for the molecular dissection of cell wall dynamics, it is necessary to distinguish individual members within a family of proteins. As a first step towards characterizing the processes involved in cell wall dynamics, we have manufactured a gene-specific 70-mer oligo microarray that consists of 765 genes classified into 30 putative families of proteins that are implicated in the cell wall dynamics of Arabidopsis. By using this array system, we identified several sets of genes that exhibit organ preferential expression profiles. We also identified gene sets that are expressed differentially at certain specific growth stages of the Arabidopsis inflorescence stem. Our results indicate that there is a division of roles among family members within each of the putative cell wall-related gene families.

Cloning, characterization and expression of OsGLN2, a rice endo-1,3-beta-glucanase gene regulated developmentally in flowers and hormonally in germinating seeds

We report here the isolation and characterization of a new endo-1,3-beta-glucanase (1,3-beta-GLU) cDNA, OsGLN2, that is expressed both in flowers and in germinating seeds of rice (Oryza sativa L.). The isolated OsGLN2 gene encoded a protein which displayed 72%, 93% and 92% identity at the amino acid level with those encoded by barley GII, rice Gns4 and glu1 1,3-beta-GLU genes, respectively. A GST-OsGLN2 recombinant protein expressed in Escherichia coli preferentially hydrolyzed Laminaria digitata 1,3;1,6-beta-glucan and liberated only oligosaccharides, suggesting that the enzyme can be classified as a 1,3-beta-GLU. Northern analysis with a 3'-UTR gene-specific probe revealed that OsGLN2 is expressed exclusively in the paleae and lemmas during flowering, and no expression of OsGLN2 was detected in other tissues such as leaf blades, leaf sheaths, stems, nodes and roots in mature rice plants. The OsGLN2 gene is also expressed in germinating seeds, where its expression is predominant in endosperms rather than embryos. In de-embryonated rice half-seeds, addition of gibberellin A3 (GA) greatly enhanced expression of the OsGLN2 gene, while the GA-induced gene expression was suppressed strongly by abscisic acid (ABA). This is the first report, to our knowledge, that OsGLN2 encodes a 1,3-beta-GLU and is expressed specifically in paleae and lemmas during flowering and in germinating seeds, where its expression is enhanced by GA and suppressed by ABA.

Cell-lytic activity of tobacco BY-2 induced by a fungal elicitor from alternaria alternata attributed to the expression of a class I beta-1,3-glucanase gene

Stress-induced cell-lytic activity was found in tobacco BY-2 cells treated with various stresses. Among 14 stresses, an elicitor fraction isolated from Alternaria alternata showed the highest inducing activity. Cell-lytic activity increased for 72 h even in the control sample, treated with distilled water, and several isozymes of beta-1,3-glucanases and chitinases were found to be involved in it. In contrast, cell-lytic activity in BY-2 cells treated with a fungal elicitor reached a higher level after 60 h. The principal enzymes specifically involved in this stress-induced portion are speculated to be basic beta-1,3-glucanases. A class I beta-1,3-glucanase gene (glu1) was found to be the specific gene for the stress-induced cell-lytic activity. Its expression became observable at 24 h, and the intensity reached a maximum at about 60-72 h. The glu1 was thus assigned as a late gene. Its role in the stress response is discussed in conjunction with earlier genes such as chitinases.

Functional analysis of a beta-1,3-glucanase gene (Tag1) with anther-specific RNA and protein accumulation using antisense RNA inhibition

A critical stage in pollen development is the dissolution of tetrads into free microspores. Tetrads are surrounded by a wall composed primarily of beta-1,3-glucan. At the completion of meiosis, tetrads are released into the anther locule after hydrolysis of the callose by a beta-1,3-glucanase complex. The cDNA corresponding to a beta-1,3-glucanase cloned from tobacco (Tag 1) represents a gene that is highly similar to other beta-1,3-glucanases and is expressed exclusively in anthers from the tetrad to free microspore stage of pollen development. Tag 1 protein was overexpressed in E. coli, accumulating in insoluble inclusion bodies. Polyclonal antibodies against Tag 1 recombinant protein identify a single 33 kD protein accumulating only in anthers at tetrad and free microspore stages where beta-1,3-glucanase activity is present. Transgenic plants expressing Tag 1 antisense RNA were produced. Although Tag 1 RNA and protein levels were greatly reduced, tetrad dissolution and pollen development were normal. These data indicate that under the conditions these tobacco plants were grown, wild type levels of Tag 1 protein are not necessary for male fertility.

Characterization and localization of the transmitting tissue-specific PELPIII proteins of Nicotiana tabacum

The class III pistil-specific PELP proteins (PELPIII) of Nicotiana tabacum includes at least two members of highly soluble glycoproteins containing glucan modules that are characteristic for arabinogalactan proteins (AGPs). PELPIII accumulates in the style transmitting tissue (TT) during pistil development and, at flower anthesis, is present in the intercellular matrix (IM) of non-pollinated pistils. After pollination, PELPIII appears to be directly and completely translocated from the IM into the pollen tube callose walls, no significant accumulation was observed in the primary wall in the tip. In the spent parts of the pollen tubes these proteins become detectable against the remnants of the tube cell membrane and in the callose plugs. Different protein extraction procedures of PELPIII from pollinated tobacco pistils showed that these proteins remain in the highly soluble protein fraction and are not modified by the growing pollen tubes. These data concur with a role in IM development and pollen tube growth. In addition, the data show that the PELPIII are able to reach the cell membrane, facilitated by an already present or induced high porosity of the tube wall and an additional, yet unknown, mechanism. The differences in behaviour between the three related classes of style IM glycoproteins of Nicotiana, namely, PELPII, TTS and the 120 kDa glycoprotein, are proposed to connect more to their differences in glycosylation than to major differences in amino acid sequence.

A pistil-specific thaumatin/PR5-like protein gene of Japanese pear (Pyrus serotina): sequence and promoter activity of the 5' region in transgenic tobacco

The genomic clone encoding the pistil-specific thaumatin/PR5-like protein (PsTL1) was isolated from Japanese pear (Pyrus serotina). Sequence analysis showed that the genomic clone contained the 5'-flanking sequence of 2.4 kb, the 3'-flanking sequence of 648 bp and the coding region interrupted by a intron of 351 bp. A sequence motif conserved in some pistil self-incompatibility gene promoters of solanaceous and brassicaceous species was located in the 5'-flanking region of the PsTL1 gene. The 2.4 kb 5'-flanking region was fused to the GUS coding sequence and transferred to tobacco. Transgenic tobacco showed GUS activity in pistil and, at low level, in anther, but not in other floral organs and leaf. Histochemical analysis localized GUS activity to stigma, transmitting tissue, anther and pollen of transgenic tobacco.

Differential expression of cell-wall-related genes during the formation of tracheary elements in the Zinnia mesophyll cell system

Plants, animals and some fungi undergo processes of cell specialization such that specific groups of cells are adapted to carry out particular functions. One of the more remarkable examples of cellular development in higher plants is the formation of water-conducting cells that are capable of supporting a column of water from the roots to tens of metres in the air for some trees. The Zinnia mesophyll cell system is a remarkable tool with which to study this entire developmental pathway in vitro. We have recently applied an RNA fingerprinting technology, to allow the detection of DNA fragments derived from RNA using cDNA synthesis and subsequent PCR-amplified fragment length polymorphisms (cDNA-AFLP), to systematically characterize hundreds of the genes involved in the process of tracheary element formation. Building hoops of secondary wall material is the key structural event in forming functional tracheary elements and we have identified over 50 partial sequences related to cell walls out of 600 differentially expressed cDNA fragments. The Zinnia system is an engine of gene discovery which is allowing us to identify and characterize candidate genes involved in cell wall biosynthesis and assembly.

Ole e 9, a Major Olive Pollen Allergen Is a 1,3-β-Glucanase

Olive pollen allergy is a clinical disorder affecting the human population of Mediterranean areas. A novel major allergen, Ole e 9, has been isolated from olive pollen by gel permeation, hydrophobic affinity, and reverse-phase high performance liquid chromatographies. It is involved in the allergic responses of 65% of patients suffering olive pollinosis. Ole e 9 (molecular mass of 46.4 kDa) displays 1,3-beta-endoglucanase activity (38.9 +/- 5.6 mg of glucose released/min x micromol of protein at pH 4.5-6.0 using laminarin as substrate). It is the first 1,3-beta-glucanase, a member of the "pathogenesis-related" protein family, detected in pollen tissue. Seven tryptic peptides of the allergen were sequenced by Edman degradation and used for designing primers to clone the cDNA codifying the protein. Specific cDNA for Ole e 9 was synthesized from total RNA and amplified using the polymerase chain reaction. The allergen sequence showed an open reading frame of 460 amino acids comprising a putative signal peptide of 26 residues. It shows 39, 33, and 32% sequence identity including the catalytic residues when compared with 1,3-beta-glucanases from wheat, willow, and Arabidopsis thaliana, respectively. Northern blot analysis showed that Ole e 9 transcript is specifically expressed in the pollen tissue, and highly conserved counterparts were only detected in taxonomically related pollens.

Three major somatic embryogenesis related proteins in Cichorium identified as PR proteins

In Cichorium hybrid clone '474' (C. intybus L., var. sativum x C. endivia L., var. latifolia), the direct somatic embryogenesis process in leaf tissues is accompanied by an overall increase in the amount of proteins secreted into the culture medium. Amongst these, three major protein bands of 38 kDa, 32 kDa and 25 kDa were found in the conditioned media. These extracellular protein bands accumulated in the medium of the embryogenic Cichorium hybrid up to 8-fold compared with those in the medium of a nonembryogenic variety. 32 and 25 kDa proteins were purified from the medium and their identities were determined as already described for 38 kDa beta-1,3-glucanases. To investigate their possible function in somatic embryogenesis, peptide sequences, serological relationships or biochemical properties revealed that there were at least two acidic chitinases of 32 kDa and one glycosylated osmotin-like protein of 25 kDa in the embryogenic culture medium. Comparing the amounts of the 38 kDa glucanases, the 32 kDa chitinases, and the 25 kDa osmotin-like protein present in the conditioned media of the embryogenic '474' hybrid and of a non-embryogenic variety, a 2-8-fold higher accumulation of these proteins was observed in the embryogenic hybrid culture medium. This may suggest that part of the accumulation of these three pathogenesis-related (PR) proteins could be correlated with the somatic embryogenesis process. Their possible involvement in this developmental process is discussed.

Molecular cloning of a soybean class III beta-1,3-glucanase gene that is regulated both developmentally and in response to pathogen infection

We isolated and characterized a soybean gene (SGN1) encoding a basic beta-1,3-glucanase that is a plant class III isoform of beta-1,3-glucanase. The deduced amino acid sequence of the SGN1 gene is similar to that of the PR-Q'b gene, the basic class III beta-1,3-glucanase of tomato. Based on RNA blot hybridization, SGN1 gene expression was detected in all tissues of 4-day old seedlings, but it was present only in root tissue of 30-day old plants. GUS expression analysis carried out in transgenic tobacco plants harboring a SGN1::GUS reporter gene revealed the same expression pattern. Furthermore, the expression of SGN1 was strongly induced by a variety of defense-related signals, such as treatment with H(2)O(2), wounding, or treatment with fungal elicitor prepared from Phytophthora spp as well as inoculation with Pseudomonas syringae. However, the expression level of SGN1 was hardly induced with jasmonate, ethephon and salicylate. Overall the results suggest that the SGN1 may play a role in both plant development and plant defense against pathogen attack.

Flower-predominant expression of a gene encoding a novel class I chitinase in rice (Oryza sativa L.)

A flower-predominant cDNA for a gene, termed OsChia 1;175, was isolated from a cDNA library of rice pistils. Northern blot and RT-PCR analyses revealed that the OsChia 1;175 gene is highly expressed in floral organs (pistils, stamens and lodicules at the heading stage) but not or at an extremely low level in vegetative organs. OsChia 1;175 encodes a protein that consists of 340 amino acid residues, and the putative mature protein shows 52% to 63% amino acid identity to class I chitinases of rice or other plants. The phylogenetic tree shows that the OsChia 1;175 protein is a new type of plant class I chitinase in rice. The expression of OsChia 1;175 in vegetative organs is not induced by several chemicals, UV, and wounding. The soluble putative mature OsChia 1;175 protein expressed in Escherichia coli exhibited chitinase activity in the assay with colloidal chitin as a substrate. Genomic Southern analysis revealed that the OsChia 1;175 gene was organized as a low-copy gene family. The rice genomic library was screened and a genome clone corresponding to OsChia 1;175 was isolated. The transcription start sites of the OsChia 1;175 gene were mapped by primer extension analysis. The 1.2 kb putative promoter region of the OsChia 1;175 gene was fused to the GUS (beta-glucuronidase) gene, and this chimeric gene was introduced to rice by Agrobacterium-mediated transformation. The flower-predominant gene expression was identified also in the transgenic rice plants. The high promoter activity was detected in the stigmas, styles, stamens and lodicules in transgenic plants. The possible functions of OsChia 1;175 are discussed.

Cloning of beta-1,3-glucanases expressed during Cichorium somatic embryogenesis

Three different beta-1,3-glucanase cDNA fragments, CG1, CG2 and CG3, were obtained by RT-PCR from RNA isolated from Cichorium hybrid '474' leaf fragments cultured for 11 days under somatic embryogenesis-inducing conditions. When expressed in Escherichia coli the proteins encoded by the three cDNAs were recognized by antibodies raised against 38 kDa extracellular beta-1,3-glucanases studied previously (Helleboid et al., Planta 205 (1998) 56-63). The CG2 and CG3 cDNAs may represent expressed alleles of one gene because their sequences showed a very high identity (98.5%) and are only 70% identical with CG1. Southern blot analysis revealed the presence of 3-4 genes coding for beta-1,3-glucanases in the Cichorium genome. Expression analysis of the genes corresponding to the three clones analysed by semi-quantitative RT-PCR indicated that CG1 mRNAs were only detectable in Cichorium hybrid '474' leaf fragments from day 3 of somatic embryogenesis induction, whereas CG2-CG3 mRNAs were already present in non-induced leaf tissue of both the embryogenic hybrid '474' and a non-embryogenic genotype. The level of CG1 mRNAs was particularly high when embryogenic cells were dividing to produce embryos, and when the amount of callose deposited in cell walls surrounding embryogenic cells and young embryos decreased. These results indicate that expression of the CG1 gene is correlated to the somatic embryogenesis process and that it encodes a 38 kDa beta-1,3-glucanase protein that may be involved in the degradation of callose localized around embryogenic cells and young embryos. A full-length CG1 cDNA clone was obtained using 3' and 5' RACE-PCR, and its sequence revealed that it encodes a beta-1,3-glucanase that is equally homologous to both class III and class IV plant beta-1,3-glucanases.

Analysis and mapping of gene families encoding beta-1,3-glucanases of soybean

Oligonucleotide primers designed for conserved sequences from coding regions of beta-1,3-glucanase genes from different species were used to amplify related sequences from soybean [Glycine max (L.) Merr.]. Sequencing and cross-hybridization of amplification products indicated that at least 12 classes of beta-1,3-glucanase genes exist in the soybean. Members of classes mapped to 34 loci on five different linkage groups using an F(2) population of 56 individuals. beta-1,3-Glucanase genes are clustered onto regions of five linkage groups. Data suggest that more closely related genes are clustered together on one linkage group or on duplicated regions of linkage groups. Northern blot analyses performed on total RNA from root, stem, leaf, pod, flower bud, and hypocotyl using DNA probes for the different classes of beta-1,3-glucanase genes revealed that the mRNA levels of all classes were low in young leaves. SGlu2, SGlu4, SGlu7, and SGlu12 mRNA were highly accumulated in young roots and hypocotyls. SGlu7 mRNA also accumulated in pods and flower buds.

A distinct member of the basic (class I) chitinase gene family in potato is specifically expressed in epidermal cells

We have isolated cDNA clones encoding class I chitinase (ChtC) from potato leaves which share a high degree of nucleotide and amino acid sequence similarity to other, previously described basic (class I) chitinases (ChtB) from potato. Despite this similarity, characteristic features distinguish ChtC from ChtB, including an extended proline-rich linker region between the hevein and catalytic domains and presence of a potential glycosylation site (NDT) in the deduced protein. These differences are in accordance with the properties of purified chitinase C which is glycosylated and hence has a higher molecular mass in comparison to chitinase B. In contrast to the coding sequences, the 3'-untranslated regions of ChtC and ChtB exhibited a low degree of similarity, which allowed us to generate gene-specific probes to study the genomic organization and expression of both types of gene. Genomic DNA blots suggest that ChtC and ChtB are each encoded by one or two genes per haploid genome. RNA blot analysis showed that in healthy potato plants ChtC mRNA is most abundant in young leaves, the organs which also contain high levels of chitinase C. By contrast, ChtB mRNA abundance is highest in old leaves, which accumulate chitinase B. By in situ RNA hybridization with gene-specific probes we could demonstrate that ChtC mRNA in leaves is restricted to epidermal cells, whereas ChtB mRNA showed no distinct pattern of cell-type-specific localization. Infection of potato leaves with Phytophthora infestans, or treatment with fungal elicitor, ethylene, or wounding resulted in accumulation of both ChtC and ChtB mRNAs; however, for ChtC, in contrast to ChtB, no corresponding accumulation of the encoded protein could be detected, suggesting a post-transcriptional mechanism of regulation. Salicylic acid treatment did not induce accumulation of either mRNA. The possible functional implications of these findings for pathogen defence and developmental processes are discussed.

A novel flower-specific Arabidopsis gene related to both pathogen-induced and developmentally regulated plant beta-1,3-glucanase genes

Beta-1,3-glucanases are usually associated with plant defense responses, although some are also developmentally or hormonally regulated. We characterized two Arabidopsis genes linked in a tandem array, BG4 and BG5, encoding putative novel isoforms of beta-1,3-glucanase. The deduced polypeptides, BG4 and BG5, were highly similar to each other (89% amino acid identity) but only moderately related (32 to 41% amino acid identity) to the different categories of previously characterized beta-1,3-glucanases, suggesting that BG4 and BG5 may represent a novel class of beta-1,3-glucanases in plants. Neither of the genes was responsive to pathogen or SA induction in contrast to the previously identified Arabidopsis beta-1,3-glucanases, nor could we detect any developmental or hormonally induced expression in the vegetative parts of the plants. Both RNA blot and in situ hybridization data demonstrated that the BG4 gene was specifically expressed in the style and septum of the ovary, suggesting that the corresponding protein is involved in the reproductive process of the plant.

The endoplasmic reticulum of plant cells and its role in protein maturation and biogenesis of oil bodies

The endoplasmic reticulum (ER) is the port of entry of proteins into the endomembrane system, and it is also involved in lipid biosynthesis and storage. This organelle contains a number of soluble and membrane-associated enzymes and molecular chaperones, which assist the folding and maturation of proteins and the deposition of lipid storage compounds. The regulation of translocation of proteins into the ER and their subsequent maturation within the organelle have been studied in detail in mammalian and yeast cells, and more recently also in plants. These studies showed that in general the functions of the ER in protein synthesis and maturation have been highly conserved between the different organisms. Yet, the ER of plants possesses some additional functions not found in mammalian and yeast cells. This compartment is involved in cell to cell communication via the plasmodesmata, and, in specialized cells, it serves as a storage site for proteins. The plant ER is also equipped with enzymes and structural proteins which are involved in the process of oil body biogenesis and lipid storage. In this review we discuss the components of the plant ER and their function in protein maturation and biogenesis of oil bodies. Due to the large number of cited papers, we were not able to cite all individual references and in many cases we refer the readers to reviews and references therein. We apologize to the authors whose references are not cited.

Transcriptional down-regulation by abscisic acid of pathogenesis-related beta-1,3-glucanase genes in tobacco cell cultures

Class I isoforms of beta-1,3-glucanases (betaGLU I) and chitinases (CHN I) are antifungal, vacuolar proteins implicated in plant defense. Tobacco (Nicotiana tabacum L.) betaGLU I and CHN I usually exhibit tightly coordinated developmental, hormonal, and pathogenesis-related regulation. Both enzymes are induced in cultured cells and tissues of cultivar Havana 425 tobacco by ethylene and are down-regulated by combinations of the growth hormones auxin and cytokinin. We report a novel pattern of betaGLU I and CHN I regulation in cultivar Havana 425 tobacco pith-cell suspensions and cultured leaf explants. Abscisic acid (ABA) at a concentration of 10 micron markedly inhibited the induction of betaGLU I but not of CHN I. RNA-blot hybridization and immunoblot analysis showed that only class I isoforms of betaGLU and CHN are induced in cell culture and that ABA inhibits steady-state betaGLU I mRNA accumulation. Comparable inhibition of beta-glucuronidase expression by ABA was observed for cells transformed with a tobacco betaGLU I gene promoter/beta-glucuronidase reporter gene fusion. Taken together, the results strongly suggest that ABA down-regulates transcription of betaGLU I genes. This raises the possibility that some of the ABA effects on plant-defense responses might involve betaGLU I.

Systemic and local induction of an Arabidopsis thionin gene by wounding and pathogens

The Arabidopsis Thi2.1 thionin gene was cloned and sequenced. The promoter was fused to the uidA gene and stably transformed into Arabidopsis to study its regulation. GUS expression levels correlated with the steady-state levels of Thi2.1 mRNA, thus demonstrating that the promoter is sufficient for the regulation of the Thi2.1 gene. The sensitivity of the Thi2.1 gene to methyl jasmonate was found to be developmentally determined. Systemic and local expression could be induced by wounding and inoculation with Fusarium oxysporum f sp. matthiolae. A deletion analysis of the promoter identified a fragment of 325 bp upstream of the start codon, which appears to contain all the elements necessary for the regulation of the Thi2.1 gene. These results support the view that thionins are defence proteins, and indicate the possibility that resistance of Arabidopsis plants to necrotrophic fungal pathogens is mediated through the octadecanoid pathway.

A pectate lyase from Zinnia elegans is auxin inducible

The Zinnia mesophyll cell system consists of isolated leaf mesophyll cells in culture that can be induced, by auxin and cytokinin, to reproducibly trans-differentiate into tracheary elements (TE) after 96 h, while in the presence of auxin alone the cells simply elongate. In a search for genes involved in modifications to cell-wall architecture before any overt signs of cell differentiation, a differential hybridization of a 72-h cDNA library with probes from mRNA at time-points of 24 h and 72 h was done revealing a number of transcripts up-regulated between these times. One of these cDNAs shows homology to pectate lyase, a pectin-degrading enzyme. The complete cDNA sequence (ZePel) corresponds to a translated protein of 44 kDa with an N-terminal signal peptide of about 2 kDa, and one potential N-glycosylation site. Northern analysis confirms that the strong expression of this gene during TE induction occurs at a very early stage of the process and is due solely to the presence of auxin in the induction medium. In situ hybridization studies in young Zinnia stems show that ZePel expression is associated with vascular bundles and shoot primordia. Recombinant protein made in Escherichia coli possesses calcium-dependent pectate lyase activity. Pectate lyase activity is detected in elongating and differentiating in vitro cell populations. The role of this enzyme in remodelling the cell wall during cell elongation and differentiation is discussed.

Primary structure and expression of acidic (class II) chitinase in potato

Infection of potato (Solanum tuberosum) leaves by the late blight fungus Phytophthora infestans or treatment with fungal elicitor leads to a strong increase in chitinase activity. We isolated cDNAs encoding acidic (class II) chitinases (ChtA) from potato leaves and determined their structures and expression patterns in healthy and stressed plants. From the total number of cDNAs and the complexity of genomic DNA blots we conclude that acidic chitinase in potato is encoded by a gene family which is considerably smaller than that encoding basic (class I) chitinase (ChtB). The deduced amino acid sequences show 78 to 96% identity to class II chitinases from related plant species tomato, tobacco) whereas the identity to basic chitinases of potato is in the range of 60%. RNA blot analysis revealed that both acidic and basic chitinases were strongly induced by infection or elicitor treatment and that the induction occurred both locally at the site of infection and systemically in upper uninfected leaves. In contrast, a differential response to other types of stress was observed. Acidic chitinase mRNA was strongly induced by salicylic acid, whereas basic chitinase mRNA was induced by ethylene or wounding. In healthy, untreated plants, acidic chitinase mRNA accumulated also in an organ-, cell-type- and development-specific manner as revealed by RNA blot analysis and in situ RNA hybridization. Relatively high transcript levels were observed in old leaves and young internodes as well as in vascular tissue and cells constituting the stomatal complex in leaves and petioles. Lower, but appreciable mRNA levels were also detectable in roots and various flower organs, particularly in sepals and stamens. The possible implications of these findings in pathogen defense, development and growth processes are discussed.

[beta]-1,3-Glucanase Is Cryoprotective in Vitro and Is Accumulated in Leaves during Cold Acclimation

We have used isolated spinach (Spinacea oleracea L.) thylakoid membranes to investigate the possible cryoprotective properties of class I [beta]-1,3-glucanase (1,3-[beta]-D-glucan 3-glucanohydrolase; EC 3.2.1.39) and chitinase. Class I [beta]-1,3-glucanase that was purified from tobacco (Nicotiana tabacum L.) protected thylakoids against freeze-thaw injury in our in vitro assays, whereas class I chitinase from tobacco had no effect under the same conditions. The [beta]-1,3-glucanase acted by reducing the influx of solutes into the membrane vesicles during freezing and thereby reduced osmotic stress and vesicle rupture during thawing. Western blots probed with antibodies directed against tobacco class I [beta]-1,3-glucanase showed that in spinach and cabbage (Brassica oleracea L.) leaves an isoform of 41 kD was accumulated during frost hardening under natural conditions.

Silencing of a beta-1,3-glucanase transgene is overcome during seed formation

Expression of a beta-1,3-glucanase transgene (gn1) driven by the CaMV 35S promoter is silenced in the T17 homozygous tobacco transgenic line. This silencing process is post-transcriptionally regulated and subject to developmental control. We have examined this phenomenon to investigate the developmental pathways involved in suppression and reactivation of gn1 expression as well as to identify the plant tissues where these processes occur. Analysis of beta-1,3-glucanase activity and gene expression have allowed us to determine that suppression of gn1 is a very efficient process reducing the steady-state gn1 mRNA level, simultaneously, in all leaves of the plant. Gene silencing occurs a few weeks after seed germination, and is maintained throughout vegetative growth and floral development. Expression of gn1 is restored in the maturing fruit some time after fertilization. In situ hybridization analyses show that expression of gn1 is restored within the developing seeds in tissues derived from meiotically divided cells. In contrast to the high level of expression found in seedlings obtained from germinated T17 homozygous seeds, the expression of gn1 is not reactivated in plantlets regenerated in vitro from leaf explants of suppressed T17 homozygous plants that is, in plant tissues obtained by mitotic division. Thus, reactivation of gn1 expression specifically occurs along the developmental programme controlling sexual reproduction and likely throughout epigenetic modifications affecting the state of gene expression during meiosis.

Pathogenesis-related functions of plant beta-1,3-glucanases investigated by antisense transformation--a review

Plant beta-1,3-glucanases (beta Glu) have been implicated in several physiological and developmental processes, e.g., cell division, microsporogenesis, pollen germination, fertilization and seed germination. These enzymes, particularly the antifungal class-I vacuolar isoforms, are also believed to be part of the defences of plants against fungal infection. The function of beta Glu in tobacco and Nicotiana sylvestris has been investigated by antisense transformation. Transformation with GLA, the gene encoding the A isoform of tobacco class-I beta Glu, in reverse orientation regulated by the strong cauliflower mosaic virus 35S RNA promoter effectively and specifically blocked the induction of class-I beta Glu. This induction was in response to ethylene treatment and following infection with the pathogenic fungus, Cercospora nicotianae, tobacco mosaic virus (TMV) and tobacco necrosis virus (TNV). Nevertheless, the plants compensated for this deficiency by producing a functionally equivalent (i.e., "ersatz') enzyme or enzymes. The fact that compensation occurred specifically in response to infection suggests that beta Glu activity has an important role in pathogenesis. Antisense transformation substantially reduced lesion size and number in virus-infected local-lesion hosts. These results suggest novel antisense-based strategies for protecting plants against virus infection. They also raise the intriguing possibility that viruses use a defence mechanism of the host, production of antifungal beta Glu, to promote their own replication and spread.

Bean ribonuclease-like pathogenesis-related protein genes (Ypr10) display complex patterns of developmental, dark-induced and exogenous-stimulus-dependent expression

The intracellular pathogenesis-related (PR) proteins of common bean (Phaseolus vulgaris L.) are encoded by a highly polymorphic family of at least 20 genes. One member, the Ypr10*c gene, has been isolated and characterised. The deduced amino acid sequence of the encoded protein, PR-10, exhibits similarities to tree-pollen allergens, to food allergens from celery and apple and to ginseng ribonuclease peptide sequences. We show by RNA blot analysis that the Ypr10 gene family, including Ypr10*c, is strongly expressed in bean roots. In leaves Ypr10 transcript levels are low in young and mature stages but are elevated during senescence and in diseased states. Dark treatment of leaves causes strong induction of Ypr10 transcripts, which is reversible by light, and diurnal rhythms of transcript accumulation during the night are observed. Ypr10 genes are responsive to external stimuli related to pathogen-defence such as glutathione or salicylic acid. Transcriptional activity of a Ypr10*c promoter-beta-glucuronidase fusion gene in transgenic tobacco was observed in roots, in developing xylem and phloem of stems, and in the blade of senescent leaves, with highest levels at the onset of senescence. The most striking characteristic of developmental expression was the specific localisation of beta-glucuronidase activity in the transmitting tract of styles in flowers at anthesis. Feeding of various pathogen-related and stress-related stimuli to young tobacco leaves led to accumulation of GUS activity in leaf blades. We identify considerable spatio-temporal similarities between reported expression patterns of Ypr10 genes and ribonuclease genes, which, together with the significant sequence similarity to the ginseng ribonuclease, support the hypothesis of a ribonuclease function for PR-10 proteins and allow the prediction of possible biological roles.

Decreased Susceptibility to Viral Disease of [beta]-1,3-Glucanase-Deficient Plants Generated by Antisense Transformation

Antifungal class I [beta]-1,3-glucanases are believed to be part of the constitutive and induced defenses of plants against fungal infection. Unexpectedly, mutants deficient in these enzymes generated by antisense transformation showed markedly reduced lesion size, lesion number, and virus yield in the local-lesion response of Havana 425 tobacco to tobacco mosaic virus (TMV) and of Nicotiana sylvestris to tobacco necrosis virus. These mutants also showed decreased severity of mosaic disease symptoms, delayed spread of symptoms, and reduced yield of virus in the susceptible response of N. sylvestris to TMV. The symptoms of disease in the responses of both plant species were positively correlated with [beta]-1,3-glucanase content in a series of independent transformants. Taken together, these results provide direct evidence that [beta]-1,3-glucanases function in viral pathogenesis. Callose, a substrate for [beta]-1,3-glucanase, acts as a physical barrier to the spread of virus. Callose deposition in and surrounding TMV-induced lesions was increased in the [beta]-1,3-glucanase-deficient, local-lesion Havana 425 host, suggesting as a working hypothesis that decreased susceptibility to virus resulted from increased deposition of callose in response to infection. Our results suggest novel means, based on antisense transformation with host genes, for protecting plants against viral infection. These observations also raise the intriguing possibility that viruses can use a defense response of the host against fungal infection[mdash]production of [beta]-1,3-glucanases[mdash]to promote their own replication and spread.

Decreased Susceptibility to Viral Disease of [beta]-1,3-Glucanase-Deficient Plants Generated by Antisense Transformation

Antifungal class I [beta]-1,3-glucanases are believed to be part of the constitutive and induced defenses of plants against fungal infection. Unexpectedly, mutants deficient in these enzymes generated by antisense transformation showed markedly reduced lesion size, lesion number, and virus yield in the local-lesion response of Havana 425 tobacco to tobacco mosaic virus (TMV) and of Nicotiana sylvestris to tobacco necrosis virus. These mutants also showed decreased severity of mosaic disease symptoms, delayed spread of symptoms, and reduced yield of virus in the susceptible response of N. sylvestris to TMV. The symptoms of disease in the responses of both plant species were positively correlated with [beta]-1,3-glucanase content in a series of independent transformants. Taken together, these results provide direct evidence that [beta]-1,3-glucanases function in viral pathogenesis. Callose, a substrate for [beta]-1,3-glucanase, acts as a physical barrier to the spread of virus. Callose deposition in and surrounding TMV-induced lesions was increased in the [beta]-1,3-glucanase-deficient, local-lesion Havana 425 host, suggesting as a working hypothesis that decreased susceptibility to virus resulted from increased deposition of callose in response to infection. Our results suggest novel means, based on antisense transformation with host genes, for protecting plants against viral infection. These observations also raise the intriguing possibility that viruses can use a defense response of the host against fungal infection[mdash]production of [beta]-1,3-glucanases[mdash]to promote their own replication and spread.

An endochitinase gene expressed at high levels in the stylar transmitting tissue of tomatoes

A gene (pMON9617; Chi2;1) identified by screening a tomato pistil cDNA library has been found to encode a protein similar in sequence to class II chitinases. Using a baculovirus expression system we show that the Chi2;1 protein is an active endochitinase. The Chi2;1 protein is most similar in sequence to a previously described stylar chitinase (SK2) isolated from potato. Both proteins lack the diagnostic N-terminal cysteine-rich regions and the C-terminal vacuolar targeting signals of class I chitinases and appear to define a novel type of class II endochitinases associated with flowers. Chi2;1 is expressed predominantly in floral organs and its expression within these organs is temporally regulated. The highest level of expression is found in the transmitting tissue of the style where Chi2;1 mRNA begins to accumulate just prior to anthesis. In vegetative tissue, low levels of Chi2;1 mRNA were detected, and these levels did not increase in response to wounding or treatment with ethephon. mRNA from Chi2;1 orthologs was not detected in most other angiosperms tested, even including some members of the Solanaceae, and it is therefore unlikely that Chi2;1 is essential for stylar function. A fragment containing 1.4 kilobase pairs of 5'-flanking DNA from the Chi2;1 gene was shown to drive high-level expression of an attached reporter gene in the styles of transgenic tomatoes. This fragment has utility for engineering expression of other coding regions in styles.

Molecular analysis of a pistil-specific gene expressed in the stigma and cortex of Solanum tuberosum

A gene, sts14, coding for a highly expressed mRNA in pistils of Solanum tuberosum, was isolated. Northern blot and in situ analyses demonstrated that the gene was expressed throughout pistil development in both the stylar cortex and the stigma. The deduced STS14 protein displays similarity to the pathogenesis-related PR-1 proteins. A possible function for protection or guidance of the pollen tubes through the pistil is discussed.