Jasmonate (JA) is an oxylipin signaling molecule that plays a crucial role in inducing plant defense mechanisms in response to herbivore feeding. During herbivore feeding, JA accumulates and induces transcriptional changes through ubiquitin-dependent degradation of JAZMONATE ZIM DOMAIN (JAZ) transcriptional repressors. A. thaliana is known to have 12 members of the JAZ family. However, a BLAST search querying JAZ8 revealed At3G22275, a gene of unknown function with sequence similarity to JAZ8. Striking domain conservation between JAZ8 and At3G22275 prompted an investigation to determine whether At3G22275 functions as a transcriptional repressor of JA responses. At3G22275 was found to interact with the JA-related transcription factor MYC2 and co-repressor TPL in a manner consistent with what has been previously reported for JAZ8. In addition, over-expression of At3G22275 dampened JA-responsive gene expression and led to a JA-insensitive phenotype during root elongation and insect feeding. Complementary to the over-expression phenotype, a loss-of-function analysis revealed JA-hypersensitivity in at3g22275/jaz10 double mutants. Interestingly, At3G22275 homologs are only found within members of the Brassicaceae family while JAZ8 homologs can be found among most land plants. Collectively, sequence similarities and experimental evidence supports the identification of At3G22275 as "JAZ13," a lineage-specific negative regulator of JA responses and a new member of the JAZ family of transcriptional repressors.
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