This was a project joint between the University of Dundee and The James Hutton Institute where both parties were interested in further understanding the interactions between plant host proteins and pathogen effector proteins. An objective of this thesis was to determine the host target of the Phytophthora infestans effector PiAVR2 and the means by which this avirulence protein is recognised by the potato resistance protein, R2. Prior to this PhD, forward genetic studies identified three RXLR effector encoding genes within the AVR2 locus. By use of transient co-expression with the resistance gene R2 it was determined which of these genes was PiAVR2. A virulent form of PiAVR2, named PiAVR2-like, was found within isolates of P. infestans. Isolates which only express PiAVR2-like are virulent on potato cultivars expressing R2. Isolates which express both forms, or only the PiAVR2 form, are avirulent on cultivars expressing R2. This suggests that expressing only PiAVR2-like is key to the virulence of the pathogen on R2 expressing cultivars. There are 10 known orthologues of R2 which all recognise PiAVR2. However none can recognise PiAVR2-like. The characterisation of the means by which P. infestans overcomes R2 resistance has provided a strategy, based on identifying R genes that recognise PiAVR2-like, to provide durable late blight disease resistance. It was also discovered that both PiAVR2 and PiAVR2-like physically interact with the same host target proteins, BSL1, BSL2a and BSL2b. The BSLs are part of a family of Kelch repeat containing Ser/Thr phosphatases which function as activators of the brassinosteroid signal transduction pathway. It was shown that silencing of the BSL1 and BSL2a genes within plants results in the attenuation of PiAVR2 recognition by R2. In the case of BSL1 it was further shown that an interaction between R2 and BSL1 only occurs in the presence of PiAVR2. This implies that R2 recognises PiAVR2 by an indirect mechanism, utilising either the Guard or Decoy Hypotheses, and that BSL1 is essential for this recognition. This is the first reported demonstration of indirect recognition of an intracellular eukaryotic plant pathogen effector protein.
|Date of Award||2012|
|Sponsors||Biotechnology and Biological Sciences Research Council|
|Supervisor||Paul Birch (Supervisor) & Eleanor Gilroy (Supervisor)|
- Phytophthora infestans