Higher plants respond to mechanical wounding and herbivory with the synthesis of the plant hormone jasmonoyl-isoleucine (JA-Ile) which in turn induces defense responses, both in local and systemic leaves. The model organism Arabidopsis thaliana has been instrumental in elucidating the JA-Ile-activated signal transduction chain, which starts with the formation of a JA-Ile-induced interaction between the F-Box protein COI1 and members of the family of JAZ repressors. COI1-mediated degradation of JAZ repressors is the key step for the activation of transcription. In this proposal, we are interested in the evolution of JA-Ile synthesis and its cognate COI1/JAZ-dependent perception. Starting point of the project is the finding that the liverwort Marchantia polymorpha genome/transcriptome contains MpCOI1 sequences, which show high similarity to AtCOI1. Amino acids which contact the ligand and/or the JAZ repressor degron are highly conserved. Moreover, a single JAZ gene encoding a degron peptide with almost the same amino acid sequence as the degron peptide of JAZs from angiosperms is present in the Marchantia genome. However, no JA or JA-Ile is detected in wounded thalli of M. polymorpha, which is consistent with the absence of the JA-Ile biosynthesis enzyme OPDA Reductase 3 (OPR3) in the publicly available genome and transcriptome sequences. In this proposal we aim to answer the following questions: (1) When during the evolution of land plants did JA biosynthesis and perception of JA-Ile by the COI1/JAZ co-receptor complex emerge? (2) What are the functions of COI1 and JAZ in M. polymorpha? (3) Is there a ligand that is perceived by the COI1/JAZ module in M. polymorpha?
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