Masters Degrees (Biochemistry)

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Browsing Masters Degrees (Biochemistry) by Author "Appel, Maryke"

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    Investigations into the production of a harpin elicitor by Pseudomonas syringae pv. syringae isolated from a nectarine tree
    (Stellenbosch : Stellenbosch University, 1996) Appel, Maryke; Bellstedt, D. U.; Stellenbosch University. Faculty of Science. Department of Biochemistry.
    ENGLISH ABSTRACT: Bacterial canker of stone fruit trees, caused by Pseudomonas syringae pv. syringae, has become one of the most destructive crop diseases in South Africa Failure of chemical control of the disease has rendered the selection and breeding of resistant host trees an important aspect of future control strategies. To assist in such breeding programmes, investigations into the molecular basis of the host-pathogen interaction were initiated The fundamental ability of phytopathogenic pseudomonads, xanthomonads and non-soft rot erwinias to cause necrotic diseases in their hosts and hypersensitivity in non-host plants is controlled by their widely conserved hrp gene clusters. The only known secreted hrp gene product, dubbed "harpin", has been identified as the molecule ("elicitor"') both responsible and required for eliciting hypersensitivity or disease symptoms. In this study, the production of a harpin elicitor by a strain of Pseudomonas syringae pv. syringae, isolated locally from nectarine tree (P. s. pv. syringae NV) was investigated. The HR test in tobacco was used to assess the elicitor activity of bacterial fractions. It was established that the bacterium produces an extracellular protein elicitor similar to harpin Pss the harpin elicitor of the wheat and bean pathogen, Pseudomonas syringae pv. syringae 61. Antibodies were raised against harpin Pss and used to confirm homology between the elicitors of the two strains, using Western blot analysis. Homology between the two proteins was exploited on the gene level in the design of a polymerase chain reaction strategy for the amplification of the harpin encoding gene of P. s. pv. syringae NV from its genomic DNA. Partial sequencing of the single PCR product and Southern blot hybridization with a probe based on the P. s. pv. syringae 61 harpin encoding gene, confirmed its identity as the harpin encoding gene of P. s pv syringae NV.