Investigating the role of the ULP-type SUMO protease ULP1a in mediating abiotic and biotic adaptive stress responses in Arabidopsis thaliana.

As global warming accelerates climate instability, sessile organisms like plants must deploy rapid adaptive mechanisms to survive unpredictable environmental changes. Post-translational modifications (PTMs), specifically SUMOylation, serve as crucial regulators that translate stress stimuli into adaptive cellular signalling. While soil salinity severely threatens global food security, the molecular mechanisms governing the salt-avoidance response in plants to survive high soil salinity, known as halotropism, remains largely unknown.

This thesis established a definitive role for SUMOylation in mediating halotropism responses in Arabidopsis thaliana (A. thaliana) through the development of the SUMO halotropism cell atlas. The atlas revealed distinct transcriptional and translational changes among SUMO components, demonstrating that halotropism fundamentally relies on deSUMOylation. Mechanistically, this research uncovers a pathway involving the ULP-type SUMO protease ULP1a, deSUMOylation, and the critical abscisic acid (ABA) regulator SnRK2.2.

Beyond abiotic stress, this work also identified a novel role for the ULP1a protease in regulating biotic stress. Utilising the high-confidence proteomic method iPAC, a ULP1a immune interactome was mapped. These findings prove that ULP1a interactors are essential in plant defence. Demonstrating that the ULP-type SUMO protease ULP1a is a central hub uniting both environmental adaptation and immune response in A. thaliana.