Dr Philip O'Brien
Position: Senior Lecturer
Research topics in general include: (1) Biology and genomics of the jarrah dieback pathogen Phytophthora cinnamomi, (including population genetics, epidemiology, mechanisms of genetic variation and mechanisms of disease). (2) mechanism of action of phosphite in protecting plants against infection by phytophthora; (3) mechanism of antifungal activity of phosphite.
Specific honours projects
These projects are part of the Centre for Phytophthora Science and Management and are carried out in collaboration with As Profs. G Hardy and B Dell, Em Prof J A McComb, and Dr T Burgess.
Genetic transformation of Phytophthora cinnamomi
To investigate the biology of the dieback pathogen, Phytophthora cinnamomi we need to be able to transform the pathogen with recombinant genes. We have successfully transformed Phytophthora cinnamomi with recombinant genes for antibiotic resistance and a fluorescent protein. However the frequency of transformation is low as the procedure has not been optimised. The aim of the project is to investigate factors that affect the transformation efficiency in an attempt to improve the efficiency. The project will be to optimise the current transformation procedure; to construct new vectors for transformation by Agrobacterium; and to analyze the phenotype of the transformants.
Biosecurity: Protecting Australia’s resources.
Exotic pathogenic microorganisms that enter Australia through the importation of contaminated germplasm have the potential to cause widespread damage to plant industries leading to the collapse of those industries. Effective quarantine depends on our ability to detect these pathogens in the absence of symptoms. This project develops methodology for the detection of species of Phytophthora in plant germplasm and soil using PCR technology. Parameters such as the sensitivity in different plant species, and specificity of the test need to be investigated.
Enzymatic measurement of phosphite
The chemical phosphite (phi) is a major weapon against the dieback pathogen Phytophthora cinnamomi. Application to plants can delay the spread of a disease front by 2-5 years. However the response of plant species to phi varies, some plants are protected whilst others are not. The degree of protection also depends on the time of application (summer vs winter). This variation may be related to differences in the distribution and persistence of phosphite in the plant. Accumulation in the roots may enhance protection as P cinnamomi is root infecting, whereas species that do not accumulate it in the roots may lose it through leaf fall. To investigate this we need a method to measure the concentration of Phi in small tissue samples. Current chemical methods to measure phi are cumbersome and expensive and require a lot of tissue. An alternative is to use an enzymatic method that is more sensitive, cheaper and allows analysis of many samples in parallel. This project will test the development of such a method based on a microbial enzyme that converts Phi to phosphate and produces NADH as a byproduct. By measureing the absorbance of NADH we can determine the amount of Phi in the sample. The method will be used to measure the accumulation of Phi in different plant tissues.
Mechanism of Action of Phosphite in protecting plants against dieback disease.
Application of the phosphate analogue phosphite to trees and understory plants protects them from infection by the dieback pathogen Phytophthora cinnamomi. Other studies have shown that phosphite treatment inhibits the Phosphate Starvation Response (PSR) in plants. Is inhibition of PSR important for protection vs infection? This project will investigate this question by using other mechanisms to inhibit PSR. The results will yield valuable information on the mechanisms by which phosphite protects the plant and will be used to develop alternatives to phosphite.
Analysis of gene expression in phosphite treated P cinnamomi.
Exposure to Phi causes inhibition of growth of Phytophthora. Knowing the mechanism by which it inhibits growth is important for understanding resistance to phosphite. The initial approach to investigate the mechanism of action is to identify the genes that are affected by Phi. In this project we will use a proteomics approach to investigate phosphite induced changes in the P cinnamomi proteome.
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