ABSTRACTTHE ROLE OF ALTERNATIVE SPLICING IN THE REGULATION OF JASMONATE SIGNALINGByLalita Chimanlal PatelThe plant hormone jasmonate (JA) is studied primarily for its role in plant defense. In response to attack by pathogens and herbivores, the JA–-amino acid conjugate JA–-isoleucine (JA–-Ile) accumulates and promotes the association of the E3 ubiquitin ligase SCFCOI1 with its substrates, the Jasmonate-ZIM domain (JAZ) repressor proteins. JAZ proteins bind the F–-box protein COI1 in a hormone–-dependent manner and are targeted for ubiquitination and degradation by the 26S proteasome pathway. JAZ degradation releases transcription factors from repression, thereby promoting transcription of JA–-responsive genes. Among the earliest response genes to be transcribed are the JAZ genes themselves. Many JAZ genes are subject to alternative splicing events that reduce the ability of JAZ proteins to interact with COI1 in a hormone–-dependent manner. These truncated JAZ proteins are hypothesized to attenuate JA responses. In this study, JAZ transcripts were quantified in response to JA elicitation and in various tissues. The results show that the relative abundance of JAZ splice variants is not significantly affected by JA elicitation or tissue type, thus suggesting that alternative splicing of JAZ pre–-mRNA is controlled by the efficiency with which cis–-acting splice sites are selected by the spliceosome. Additionally, transgenic plants ectopically expressing cDNAs encoding truncated splice variants of JAZ2 and JAZ4 have reduced sensitivity to JA, indicating that these proteins act as dominant repressors of JA signaling. This research highlights the importance of alternative splicing as an adaptive response of plants to environmental stress.
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