Programmed Cell Death in the model organisms Chlamydomonas reinhardtii and Arabidopsis thaliana

Background: Programmed Cell Death (PCD) is the genetically controlled death of specific cells following developmental or environmental stimuli. There is potential for PCD to be manipulated through genetic engineering to increase productivity in commercially relevant plant and algae species. KISS OF DEATH (KOD) has been identified as a short peptide involved in the regulation of PCD in Arabidopsis thaliana. Increasing our knowledge of KOD and PCD in general could lead to important innovations in biotechnology. Methods: We investigated the potential of Cell Penetrating Peptides (CPPs) as a tool to assay potential short peptides in microalgae and protoplasts, in the model organisms Chlamydomonas reinhardtii and A. thaliana. We also heterologously expressed KOD in C. reinhardtii to gain further insights into microalgal PCD. Finally, we screened for and tested KOD homologues in A. thaliana. Results: Data from study of CPPs indicates that CPPs may not be suitable for the study of PCD in microalgae as they induce cell death even without a cargo. The expression of KOD in C. reinhardtii led to unexpected results. It was found that liquid cultures, which expressed KOD, maintained cell density in stationary phase for longer periods than controls. This suggests that the heterologous expression of KOD in C. reinhardtii prevented cell death. A KOD homologue was identified which had a PCD sensitive phenotype, providing more evidence for the role of small peptides in PCD. Conclusion: This thesis has provided further insights into the mechanisms of PCD in plants and algae; however, more work is required to develop our knowledge further before PCD can be manipulated to increase the productivity of plants and algae through biotechnology.