| The plant hormone jasmonate (JA) regulates a wide range of growth, developmental, and defense-related processes. Recently, JASMONATE ZIM-domain (JAZ) proteins were identified as negative regulators of transcription factors that control the expression of JA-response genes. Upon perception of bioactive JA derivatives by the F-box protein CORONATINE INSENSITIVE I (COI1), JAZ proteins are degraded via the SCFCOI1/ubiquitin/26S proteasome pathway, thereby relieving the restraint on JA-response genes. A highly conserved "dergon" sequence, referred to as the Jas domain, mediates the JA-dependent interaction of JAZ proteins with COI1. The broad aim of this thesis research is to further understand the molecular mechanism by which JAZ proteins regulate the JA signal transduction pathway. To address this objective, the effect of wounding, insect herbivory, and cycloheximide on the expression level of Arabidopsis JAZ genes was determined. The results showed that most JAZ genes are rapidly induced by tissue damage, and that JAZs are primary response genes whose expression is activated upon turnover of labile repressor proteins. Transgenic plants that overexpress a truncated form of JAZ1 lacking the Jas domain were compromised in resistance to the generalist herbivore Spodoptera exigua, suggesting a role for JAZ proteins in the regulation of anti-insect defenses. It was also shown that the plant-specific ZIM domain mediates JAZ homo-and heteromeric interactions, and that these interactions are essential for the repressive function of JAZ. Molecular characterization of three JAZ10 splice variants showed that alternative splicing events affecting the Jas domain alter the in vivo stability of JAZ proteins by modifying their ability to interact with SCFCOI1. Comparative analysis of JAZ genes from diverse plant species identified an evolutionarily conserved intron whose retention during pre-mRNA splicing contributes to functional diversification of JAZ proteins through altered protein stability. |
