Subtractive hybridisation

• Introduction
• Pathogenesis, secretion systems
• Defence + hypersensitive reaction
• Horizontal transfer, pathogenicity islands + clustering
• Arms races, hypervariability
• Methods
• Fragment, denature, hybridise, clone + select, amplify, sequence
• Results/discussion
• Table of genes found and potential roles

Plant pathogens cause disease by attaching to host cells and secreting effectors (toxins) into the cytoplasm. Several mechanisms -- secretion systems -- facilitate this. Plants, in return, have a number of defence mechanisms, such as the hypersensitive response, in which apoptosis is triggered in order to prevent spread of the disease. As the first signs of infection, the secretion systems are often the triggers of plant defence mechanisms, and evolutionary arms races create great variation in these regions. Additionally, pathogenicity islands (clusters of virulence genes), including those involved in secretion systems, are known to be horizontally transferred between bacterial species.