Isolation and purity determination of a glycoprotein elicitor from wheat stem rust by medium-pressure liquid chromatography

The protein elicitor Hrip1 enhances resistance to insects and early bolting and flowering in Arabidopsis thaliana

The elicitor Hrip1 isolated from necrotrophic fungus Alternaria tenuissima, could induce systemic acquired resistance in tobacco to enhance resistance to tobacco mosaic virus. In the present study, we found that the transgenic lines of Hrip1-overexpression in wild type (WT) Arabidopsis thaliana were more resistant to Spodoptera exigua and were early bolting and flowering than the WT. A profiling of transcription assay using digital gene expression profiling was used for transgenic and WT Arabidopsis thaliana. Differentially expressed genes including 40 upregulated and three downregulated genes were identified. In transgenic lines of Hrip1-overexpression, three genes related to jasmonate (JA) biosynthesis were significantly upregulated, and the JA level was found to be higher than WT. Two GDSL family members (GLIP1 and GLIP4) and pathogen-related gene, which participated in pathogen defense action, were upregulated in the transgenic line of Hrip1-overexpression. Thus, Hrip1 is involved in affecting the flower bolting time and regulating endogenous JA biosynthesis and regulatory network to enhance resistance to insect.

Inducible and constitutive expression of an elicitor gene Hrip1 from Alternaria tenuissima enhances stress tolerance in Arabidopsis

Hrip1 is a novel hypersensitive response-inducing protein secreted by Alternaria tenuissima that activates defense responses and systemic acquired resistance in tobacco. This study investigates the role that Hrip1 plays in responses to abiotic and biotic stress using transgenic Arabidopsis thaliana expressing the Hrip1 gene under the control of the stress-inducible rd29A promoter or constitutive cauliflower mosaic virus 35S promoter. Bioassays showed that inducible Hrip1 expression in rd29A∷Hrip1 transgenic lines had a significantly higher effect on plant height, silique length, plant dry weight, seed germination and root length under salt and drought stress compared to expression in 35S∷Hrip1 lines and wild type plants. The level of enhancement of resistance to Botrytis cinerea by the 35S∷Hrip1 lines was higher than in the rd29A∷Hrip1 lines. Moreover, stress-related gene expression in the transgenic Arabidopsis lines was significantly increased by 200 mM NaCl and 200 mM mannitol treatments, and defense genes in the jasmonic acid and ethylene signaling pathway were significantly up-regulated after Botrytis inoculation in the Hrip1 transgenic plants. Furthermore, the activity of some antioxidant enzymes, such as peroxidase and catalase increased after salt and drought stress and Botrytis infection. These results suggested that the Hrip1 protein contributes to abiotic and biotic resistance in transgenic Arabidopsis and may be used as a useful gene for resistance breeding in crops. Although the constitutive expression of Hrip1 is suitable for biotic resistance, inducible Hrip1 expression is more responsive for abiotic resistance.

In situ detection of a fungal glycoprotein-elicitor in stem rust-infected susceptible and resistant wheat using immunogold electron microscopy

Immunoelectron microscopy (IEM) was used to analyze the compatible and incompatible host-pathogen interaction between the obligate, biotroph stem rust (Puccinia graminis f.sp. tritici; Pgt) and primary leaves of wheat (Triticum aestivum L.). The investigation was focused on the subcellular localization of a fungal elicitor glycoprotein of stem rust (Pgt-elicitor). Uredospores as well as fungal infection structures of stem rust on wheat leaves were probed with a specific monoclonal antibody, in order to determine the in situ distribution pattern of the antigen. Binding to the anti-elicitor antibody was observed over the cell wall and the germ pore of germinating uredospores. Immunogold staining was found over the infection structures of stem rust within the wheat leaf tissue of both the compatible and incompatible plant-pathogen interaction. Distinct cell wall layers of the intercellular mycelium, of the haustorial mother cells, as well as of the haustoria were clearly labeled. Gold particles were also detected over the intercellular space and the extrahaustorial matrix in between the extrahaustorial membrane and the haustorial cell wall which indicated a release of elicitor molecules from the fungal cell wall. No labeling was observed over the host cell cytoplasm of the compatible and incompatible interaction, respectively. The immunocytochemical detection of elicitor epitopes over the hyphal cell walls of in vitro grown axenic cultures of P. graminis f.sp. tritici confirmed the occurrence of elicitor molecules in young hyphal material. Elicitor molecules were released by the hyphae of axenic cultures of stem rust in vitro.

Microbial elicitors and their receptors in plants

Elicitors are molecules that stimulate any of a number of defense responses in plants. Research over the past decade has focused on the mechanisms by which plant cells perceive and transduce these biological signals to activate defense responses. Of particular interest has been the identification of specific elicitor-binding proteins that might function as physiological receptors in the signal transduction cascade. The existence of specific high-affinity binding sites has been demonstrated for oligosaccharide, glycopeptide, and peptide elicitors, and candidate elicitor-binding proteins have been identified for several of them. The properties of these binding sites/proteins are consistent with those expected of physiologically important receptors, although experimental verification of the role of these binding proteins as receptors has not yet been obtained. The purification and characterization of specific elicitor-binding proteins is essential for a detailed understanding of the molecular basis for the signal exchange between plant hosts and microbial pathogens that leads to activation of host defenses.

Purification of cytochromes P-450 derived from liver microsomes of untreated and 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated marmoset monkeys

The purification of multiple forms of cytochrome P-450 (P450) from 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-treated marmosets using fast protein liquid chromatography (FPLC) is described. The main aim was to achieve a better separation of certain closely related P450 sub-forms from each other than that previously obtained using conventional chromatography. An 8-aminooctyl-Sepharose fraction of cholate-solubilized microsomes was obtained first and, after fast desalting on Sephadex G-25, loaded on to a preparative Mono Q column. Five of the six gradient peaks contained P450 and were each rechromatographed on an analytical Mono Q column. The pass-through peak was fractionated further using a Mono S column. Other HPLC-quality anion- and cation-exchange gels were compared. For removal of excess of non-ionic detergent, five types of hydroxyapatite gels were compared. Seven purified forms of P450 and cytochrome b5 and P420 were isolated and characterized according to PHAST sodium dodecylsulphate-polyacrylamide gel electrophoretic apparent molecular masses, catalytic, spectral and magnetic properties and also TCDD-binding capacity (molar ratio of [14C]TCDD to P450). There are at least two sub-forms which appear to be TCDD inducible, one showing a substantial ethoxyresorufin-O-deethylase activity and the other having a high TCDD-binding molar ratio. Two other forms appear to be constitutive, as deduced from comparisons with forms purified from untreated animals.