Characterization of two class II chitinase genes from peanut and expression studies in transgenic tobacco plants

Bioinformatics and Expression Analysis of the Chitinase Genes in Strawberry (Fragaria vesca) and Functional Study of FvChi-14

Plant chitinases (EC 3.2.1.14) are pathogenesis-related (PR) proteins and are well studied in many plant species. However, little is known about the genomic organization and expression of chitinase genes in strawberries (Fragaria vesca). Here, 23 FvChi genes were identified in the genome of strawberry (F. vesca) and divided into GH18 and GH19 subfamilies based on phylogenetic relationships. A detailed bioinformatics analysis of the FvChi genes was performed, including gene physicochemical properties, chromosomal location, exon-intron distribution, domain arrangement, and subcellular localization. Twenty-two FvChi genes showed upregulation after Colletotrichum gloeosporioides infection. Following the exogenous application of SA, FvChi-3, 4, and 5 showed significant changes in expression. The ectopic expression of FvChi-14 in Arabidopsis thaliana increased resistance to C. higginsianum via controlling the SA and JA signaling pathway genes (AtPR1, AtICS1, AtPDF1.2, and AtLOX3). The FvChi-14 protein location was predicted in the cell wall or extracellular matrix. We speculate that FvChi-14 is involved in disease resistance by regulating the SA and JA signaling pathways. The findings of this study provide a theoretical reference for the functional studies of FvChi genes and new candidates for strawberry stress resistance breeding programs.

Molecular characterization of stress resistance-related chitinase genes of Brassica rapa

Brassica is an important vegetable group worldwide that is impacted by biotic and abiotic stresses. Molecular biology techniques offer the most efficient approach to address these concerns. Inducible plant defense responses include the production of pathogenesis-related (PR) proteins, and chitinases are very important PR proteins. We collected 30 chitinase like genes, three from our full-length cDNA library of Brassica rapa cv. Osome and 27 from Brassica databases. Sequence analysis and comparison study confirmed that they were all class I-V and VII chitinase genes. These genes also showed a high degree of homology with other biotic stress resistance-related plant chitinases. An organ-specific expression of these genes was observed and among these, seven genes showed significant responses after infection with Fusarium oxysporum f.sp. conglutinans in cabbage and sixteen genes showed responsive expression after abiotic stress treatments in Chinese cabbage. BrCLP1, 8, 10, 17 and 18 responded commonly after biotic and abiotic stress treatments indicating their higher potentials. Taken together, the results presented herein suggest that these chitinase genes may be useful resources in the development of stress resistant Brassica.

Tomato polyphenol oxidase B is spatially and temporally regulated during development and in response to ethylene

Plant polyphenol oxidases (PPOs) are ubiquitous plastid-localized enzymes. A precise analysis of PPO function in plants has been complicated by the presence of several family members with immunological cross reactivity. Previously we reported the isolation of genomic clones coding for the seven members of the tomato (Solanum lycopersicum) PPO family (A, A', B, C, D, E, and F). Here we report the complex spatial and temporal expression of one of the members, PPO B. The PPO B promoter was sequenced and subjected to homology analysis. Sequence similarities were found to nucleotide sequences of genes encoding enzymes/proteins active in the following systems: phenylpropanoid biosynthesis, signal transduction and responsiveness to hormones and stresses, fruit and seed proteins/enzymes, and photosynthesis. Chimeric gene fusions were constructed linking PPO B 5' flanking regions to the reporter gene, b-glucuronidase (GUS). The resultant transgenic plants were histochemically analyzed for GUS activity in various vegetative and reproductive tissues, and evaluated for PPO B responsiveness to ethylene induction. It was shown that PPO B expression was tissue specific, developmentally regulated, ethylene induced, and localized predominantly to mitotic or apoptotic tissues.

Chitinases in Oryza sativa ssp. japonica and Arabidopsis thaliana

Chitinases (EC3.2.1.14), found in a wide range of organisms, catalyze the hydrolysis of chitin and play a major role in defense mechanisms against fungal pathogens. The alignment and typical domains were analyzed using basic local alignment search tool (BLAST) and simple modular architecture research tool (SMART), respectively. On the basis of the annotations of rice (Oryza sativa L.) and Arabidopsis genomic sequences and using the bio-software SignalP3.0, TMHMM2.0, TargetP1.1, and big-Pi Predictor, 25 out of 37 and 16 out of 24 open reading frames (ORFs) with chitinase activity from rice and Arabidopsis, respectively, were predicted to have signal peptides (SPs), which have an average of 24.8 amino acids at the N-terminal region. Some of the chitinases were secreted extracellularly, whereas some were located in the vacuole. The phylogenic relationship was analyzed with 61 ORFs and 25 known chitinases and they were classified into 6 clusters using Clustal X and MEGA3.1. This classification is not completely consistent when compared with the traditional system that classifies the chitinases into 7 classes. The frequency of distribution of amino acid residues was distinct in different clusters. The contents of alanine, glycine, serine, and leucine were very high in each cluster, whereas the contents of methionine, histidine, tryptophan, and cysteine were lower than 20%. Each cluster had distinct amino acid characteristics. Alanine, valine, leucine, cysteine, serine, and lysine were rich in Clusters I to VI, respectively.

Over-expression of a cacao class I chitinase gene in Theobroma cacao L. enhances resistance against the pathogen, Colletotrichum gloeosporioides

Theobroma cacao L. plants over-expressing a cacao class I chitinase gene (TcChi1) under the control of a modified CaMV-35S promoter were obtained by Agrobacterium-mediated transformation of somatic embryo cotyledons. Southern blot analysis confirmed insertion of the transgene in eight independent lines. High levels of TcChi1 transgene expression in the transgenic lines were confirmed by northern blot analysis. Chitinase activity levels were measured using an in vitro fluorometric assay. The transgene was expressed at varying levels in the different transgenic lines with up to a sixfold increase of endochitinase activity compared to non-transgenic and transgenic control plants. The in vivo antifungal activity of the transgene against the foliar pathogen Colletotrichum gloeosporioides was evaluated using a cacao leaf disk bioassay. The assay demonstrated that the TcChi1 transgenic cacao leaves significantly inhibited the growth of the fungus and the development of leaf necrosis compared to controls when leaves were wound inoculated with 5,000 spores. These results demonstrate for the first time the utility of the cacao transformation system as a tool for gene functional analysis and the potential utility of the cacao chitinase gene for increasing fungal pathogen resistance in cacao.

Promoter activation of pepper class II basic chitinase gene, CAChi2, and enhanced bacterial disease resistance and osmotic stress tolerance in the CAChi2-overexpressing Arabidopsis

The activation of the CAChi2 promoter as the result of bacterial infection and osmotic stresses was examined using the Agrobacterium-mediated transient expression assay. Several stress-related cis-acting elements were revealed within the upstream genomic sequence of the CAChi2 gene. In tobacco leaf tissues transiently transformed with the CAChi2 promoter-beta-glucuronidase (GUS) gene, the CAChi2 promoter was up-regulated by Pseudomonas syringae pv. tabaci infection. The CAChi2-GUS activation was closely related to osmotic stresses, including treatment with mannitol and NaCl. The -378 CAChi2 promoter was sufficient for the CAChi2 gene induction by salicylic acid treatment. CAChi2 overexpression in the transgenic Arabidopsis plants enhanced bacterial disease resistance against Pseudomonas syringae pv. tomato infection. CAChi2-overexpressing Arabidopsis plants also exhibited increased tolerance to NaCl-induced osmotic stresses during seed germination and seedling growth. CAChi2 overexpression induced the expression of the NaCl stress-responsive gene RD29A in the absence of NaCl stress. The CAChi2-overexpressing transgenic plants exhibited increased sensitivity to abscisic acid during seed germination.

beta-1,3-Glucanase Activity in Peanut Seed (Arachis hypogaea) is Induced by Inoculation with Aspergillus flavus and Copurifies with a Conglutin-Like Protein

ABSTRACT Infection of peanut (Arachis hypogaea) seed by Aspergillus flavus and A. parasiticus is a serious problem that can result in aflatoxin contamination in the seed. Breeding resistant cultivars would be an effective approach to reduce aflatoxin accumulation. The objective of this study was to investigate the expression of the pathogenesis-related (PR) protein beta-1,3-glucanase and the isoform patterns in peanut seed inoculated with A. flavus. Peanut genotypes GT-YY9 and GT-YY20 (both resistant to A. flavus infection) and Georgia Green and A100 (both susceptible to A. flavus infection) were used in this study. The activities of beta-1,3-glucanase were similar in the uninfected seed of all genotypes, but increased significantly in the resistant genotypes after inoculation in comparison with the susceptible genotypes. An in-gel (native polyacrylamide gel electrophoresis [PAGE]) enzymatic activity assay of beta-1,3-glucanase revealed that there were more protein bands corresponding to beta-1,3-glucanase isoforms in the infected seed of resistant genotypes than in the infected seed of susceptible genotypes. Both acidic and basic beta-1,3-glucanase isoforms were detected in the isoelectric focusing gels. Thin-layer chromatography analysis of the hydrolytic products from the reaction mixtures of the substrate with the total protein extract or individual band of native PAGE revealed the presence of enzymatic hydrolytic oligomer products. The individual bands corresponding to the bands of beta-1,3-glucanase isoforms Glu 1 to 5 were separated on the sodium dodecyl sulfate-PAGE, resulting in two bands of 10 and 13 kDa, respectively. The sequences of fragments of the 13-kDa major protein band showed a high degree of homology to conglutin, a storage protein in peanut seed. Conglutin is reported as a peanut allergen, Ara h2. Our data provide the first evidences for peanut having beta-1,3-glucanase activities and the association with the resistance to A. flavus colonization in peanut seed. We have not directly demonstrated that conglutin has beta-1,3-glucanase activity.

ArabidopsisChitinases: a Genomic Survey

Plant chitinases (EC 3.2.1.14) belong to relatively large gene families subdivided in classes that suggest class-specific functions. They are commonly induced upon the attack of pathogens and by various sources of stress, which led to associating them with plant defense in general. However, it is becoming apparent that most of them display several functions during the plant life cycle, including taking part in developmental processes such as pollination and embryo development. The number of chitinases combined with their multiple functions has been an obstacle to a better understanding of their role in plants. It is therefore important to identify and inventory all chitinase genes of a plant species to be able to dissect their function and understand the relations between the different classes. Complete sequencing of the Arabidopsis genome has made this task feasible and we present here a survey of all putative chitinase-encoding genes accompanied by a detailed analysis of their sequence. Based on their characteristics and on studies on other plant chitinases, we propose an overview of their possible functions as well as modified annotations for some of them.

Transformation of peanut (Arachis hypogaea L.) with tobacco chitinase gene: variable response of transformants to leaf spot disease

Fertile transgenic plants of peanut (Arachis hypogaea L.) cv. TMV-2 expressing tobacco chitinase and neomycin phosphotransferase (npt II) genes were generated using an Agrobacterium tumefaciens (LBA4404/pBI121-pBTex)-mediated transformation system. A tissue culture-independent method wherein embryo in the mature seed is inoculated and reared into single plant transformant was used for transformation. Southern blot analysis of genomic DNA isolated from T(0) transformants and progeny plants (T(1)) demonstrated that the transgenes are stably integrated in the genome of transgenic peanut plants and inherited by the offspring. The expression of the heterologous chitinase gene driven by CaMV 35S promoter led to a high level of activity in some of the transgenic plants. Small-scale field tests indicated increased ability of these plants to resist the fungal pathogen Cercospora arachidicola (the causal organism of the leaf spot or Tikka disease of peanut), which is an important peanut pathogen. These results suggest that a heterologous chitinase gene was functional in peanut and expressed in healthy plants. The study also shows that peanut plants containing transgenically increased activity of chitinase were resistant to attack by the fungal pathogen C. arachidicola to different degrees. The strategy employed may be useful for the control of other fungal diseases of the crop.

Two differentially regulated class II chitinases from parsley

Two distinct cDNA clones, PcCHI1 and PcCHI2, with high sequence similarity to plant chitinases were isolated from parsley (Petroselinum crispum), expressed in Escherichia coli, and the encoded proteins functionally identified as endochitinases. Different expression patterns of the corresponding mRNAs and proteins in infected and uninfected parsley plants indicated distinct roles of the two isoforms in both pathogen defense and plant development. Infection of parsley leaf buds with Phytophthora sojae resulted in the rapid, transient and highly localized accumulation of PcCHI1 mRNA and protein around infection sites, whereas PcCHI2 mRNA and protein were systemically induced at later infection stages. Similar differences in the timing of induction were observed in elicitor-treated, suspension-cultured parsley cells. In uninfected plants, PcCHI1 mRNA was particularly abundant in the transmitting tract of healthy flowers, suggesting a role in the constitutive protection of susceptible transmitting tissue of the style against pathogen ingress and/or in the fertilization process, possibly by affecting pollen tube growth. Localization of PcCHI2 mRNA and protein in the parenchymatic collenchyme of young pedicels may indicate a function in the constitutive protection of this tissue. In addition to such distinct roles of PcCHI1 and PcCHI2 in preformed and induced pathogen defense, both chitinases may have endogenous regulatory functions in plant development.

The movement protein NSm of tomato spotted wilt tospovirus (TSWV): RNA binding, interaction with the TSWV N protein, and identification of interacting plant proteins

The nonstructural NSm protein of tomato spotted wilt tospovirus (TSWV) represents a putative viral movement protein involved in cell-to-cell movement of nonenveloped ribonucleocapsid structures. To study the molecular basis of NSm function, we expressed the protein in Escherichia coli and investigated protein-protein and protein-RNA interactions of NSm protein in vitro. NSm specifically interacts with TSWV N protein and binds single-stranded RNA in a sequence-nonspecific manner. Using NSm as a bait in a yeast two-hybrid screen, we identified two homologous NSm-binding proteins of the DnaJ family from Nicotiana tabacum and Arabidopsis thaliana.

Carica papaya latex is a rich source of a class II chitinase

A class II chitinase is present in the latex of the tropical species Carica papaya. The enzyme may be readily purified by using a combination of hydrophobic interaction- and cation-exchange chromatography. This enzyme preparation is homogeneous with respect to the three physico-chemical criteria of charge, M(r) (28,000) and hydrophobicity. It is also completely free of any proteolytic and bacteriolytic activities. The enzyme was classified as a class II chitinase on the basis of its N-terminal amino acid sequence up to the 30th residue. In agreement with this classification, the enzyme preparation hydrolyses chitinase substrates only very slowly and several free thiol functions are present in the polypeptide chain. These free thiol functions are buried, and to be available for titration with 2,2'-dipyridyldisulphide, the enzyme must be denatured. Unfolding of papaya chitinase requires particularly drastic conditions, not less than 4 M guanidinium hydrochloride at 25 degrees and pH 6.8.