Understanding JA desensitization through the study of a JAZ splice variant resistant to COI1-mediated degradation

JAVIER MORENO; GREGG HOWE

Madison

Conferencia; 22nd International Conference on Arabidopsis Research; 2011

The North American Arabidopsis Steering Committee

Jasmonate (JA), a lipid-derived hormone, modulates myriad plant responses involved in growth, development, and defense. JA- induced plant responses are negatively regulated by JASMONATE-ZIM DOMAIN (JAZ) proteins that bind to and inhibit bHLH-type transcription factors such as MYC2. The presence of JA-Ile, the bioactive hormone, is perceived by a receptor complex consisting of JAZ and the F-box protein CORONATINE INSENSITIVE 1 (COI1). In this way, JA-Ile imparts specificity to an E3-ubiquitin ligase complex (SCFCOI1) that targets JAZ proteins for degradation, thereby unleashing JA responses. JAZ proteins share a conserved region known as the Jas domain. This domain is required for JAZ interaction with both COI1 and MYC2. Interestingly, some JAZ genes undergo alternative splicing events that truncate or remove the Jas domain. These splice variants are resistant to COI1-mediated degradation but still retainthe ability to interact with and repress MYC2. Plants that overexpress these splice variants show decreased sensitivity to JA. We are using the JAZ10.4 splice variant to study the physiological relevance of JAZ alternative splicing. Although JAZ10.4 lacks the entire Jas domain, this protein retains the ability to interact with MYC2 in vitro and in vivo. Site-directed and deletion mutagenesis experiments were used to define the MYC2-binding motif in JAZ10.4. Deletion of this domain impaired the ability of JAZ10.4 to repress JA responses when overexpressed in Arabidopsis. Given that JAZ10.4 accumulates after JA treatment, we propose a model in which active repression of MYC2 by JAZ10.4 modulates JA responses in the presence of high intracellular levels of JA-Ile. Such a mechanism may serve to maximize the plasticity of JA responses and reduce the deleterious effects of JA on plant growth.