Understanding the role of JASMONATE ZIM DOMAIN proteins in plant stress response and development

Climate change deeply affects plant life and consequently life on the entire planet earth. Exposure to constant environmental change has led plants to develop signalling pathways to balance growth and defence responses. Multiple signalling molecules regulate the mechanisms through which plants respond to external cues. Jasmonates (JAs) regulate a plethora of developmental processes and activate defence mechanisms in plants. In response to JAs perception, plant cells activate a significant reprograming of gene expression downstream inducing the production of specialized metabolites. The JASMONATE ZIM DOMAIN (JAZ) proteins are targets of the SCFCOI1 JA co-receptor and are degraded via the 26S proteasome. Besides their well-known role as negative regulators of JA responses, JAZ proteins have also been identified in orchestrating the crosstalk between JA and other hormone signalling pathways such as ethylene (ET), gibberellic acid (GA), salicylic acid (SA), abscisic acid (ABA) and auxin. The main aim of this project was to understand the role of JAZ proteins in growth and stress responses and development in model plants using physiological and gene editing techniques.

Existing Arabidopsis thaliana mutant lines were used in this work. Application of exogenous JA as well as mannitol, to mimic response to osmotic stress, showed differences between lines in root growth, rosette size and gene expression. Moreover, measurement of total phenolic content under exogenous JA treatment in seedlings and cell suspension cultures, provided further information on the role of JAZ genes in stress response in presence or absence of organ developmental control. Associations between core components of the JA-signalling pathway including the COI1 receptor and JAZs repressors to these phenotypical changes were reinforced. Additionally, a link between COI1 and phytochrome B (PHYB) to JAZ was observed under osmotic stress conditions.

Diverse genome editing methods in plants have been rapidly expanding to target specific loci regions. CRISPR/Cas9 has proved to be exceptionally valuable for high- throughput genome engineering. The generation of CRISPR/Cas9 plasmids was achieved in this work, for the modification of specific JAZ proteins in Arabidopsis thaliana and Solanum lycopersicum plants. Prediction of edited templates in the desired genes alongside protein structure models provided relevant information that helped to understand the role of JAZ’s in stress and developmental traits. Factors affecting the transformation process of model plants are discussed in this work.