Jasmonates (JAs) are plant hormones that regulate defense against microbial pathogens and insect herbivores via two antagonistic branches of the JAs signaling pathway leading to activation of... Show moreJasmonates (JAs) are plant hormones that regulate defense against microbial pathogens and insect herbivores via two antagonistic branches of the JAs signaling pathway leading to activation of distinct sets of defense genes. In Arabidopsis thaliana defense against herbivores is regulated by JAs alone which act via the receptor COI1 to cause degradation of Jasmonate-ZIM (JAZ) repressors thereby leading to activation of MYC transcription factors. In defense against microbial pathogens, JAs synergize with ethylene (ET). The APETALA2/Ethylene Response Factor (AP2/ERF)-domain transcription factor ORA59 integrates the JAs/ET signaling pathways and regulates resistance against necrotrophic pathogens. In search for ORA59-interacting proteins we found the CCCH zinc finger proteins ZFAR1 and ZFAR2, which in turn interacted with the JAs-responsive repressor JAZ1 to repress ORA59 activity. Gibberellins (GAs) modulate JA/ET signaling depending on DELLAs, key repressors of GA signaling. Here, we show that DELLAs directly interact in vivo and in vitro with ZFAR1, ZFAR2, and JAZ1. DELLAs repress the activity of ZFAR and JAZ1, and, thereby, enhance the activity of ORA59 resulting in higher expression levels of its target genes including PDF1.2. Thereby we provide a unifying model for the role of the JAZ repressors in the pathogen and herbivore branches of JAs signaling. Show less
Plants produce a variety of secondary metabolites. In Catharanthus roseus, several have pharmaceutical applications, including the monomeric alkaloids serpentine and ajmalicine, which are used as a... Show morePlants produce a variety of secondary metabolites. In Catharanthus roseus, several have pharmaceutical applications, including the monomeric alkaloids serpentine and ajmalicine, which are used as a tranquillizer and to reduce hypertension, respectively, and the dimeric alkaloids vincristine and vinblastine, which are potent antitumour drugs. Jasmonic acid (JA) is a key defense hormone, which controls the expression of several alkaloid biosynthesis genes in Catharanthus. The JA-responsive expression is controlled by the AP2-domain transcription factors ORCA2 and ORCA3. The results in this thesis demonstrate that JA-responsive ORCA expression is controlled by an up-stream positive regulator, whose activities are affected by a family of repressors. Understanding the regulation mechanism may help to generate a very valuable tool for engineering the production of valuable secondary metabolites. Show less
