An investigation into the role of the ubiquitin-proteasome system in plant defence

Ubiquitin is a highly conserved regulatory protein that is ubiquitously expressed in eukaryotes. The ubiquitin pathway appears to be more diversified in plants compared to the other organisms. In plants, the ubiquitin-26S proteasome pathway appears to be particularly involved in regulating plant growth, development and defence signalling. This project is concerned with establishing potential involvement of UBP12 and UBP13 in plant defence. The Arabidopsis-Pseudomonas interaction was employed to examine the transcriptional response of AtUBP12 and AtUBP13 during pathogen infection. Furthermore, a transient over expression approach was used to investigate possible gain of function phenotypes associated with NtUBP12 (tobacco homologue of AtUBP12 and AtUBP13) activity during Cf-9 triggered HR in tobacco. The second objective of this study was to identify the interactor of UBP12 by employing a yeast two hybrid screen. The final objective was to analyse the functional significance of the mutant forms of ubiquitin during ubiquitination of target protein. Added to the above-mentioned objectives, this study also details the production of plant anti-ubiquitin antibody. The data presented in this study suggests that UBP12 and UBP13 play a critical role in plant defence. The yeast two hybrid assays showed that DIN1 is the interactor of UBP12. The analysis mutant forms of ubiquitin did not show any considerable difference in the pattern of in vitro ubiquitination compared to the wild type ubiquitin; the probable reasons for this were discussed. The anti-ubiquitin antibody generated in this study was shown to have affinity against plant and human ubiquitin