The study investigates the role of NINJA, a previously uncharacterized protein, in jasmonate signaling in plants. NINJA is shown to interact with JAZ proteins, which are repressors of gene expression in response to jasmonate. The interaction between NINJA and JAZ proteins is mediated by the TIFY motif of JAZ proteins and the C-terminal domain of NINJA. NINJA also interacts with the Groucho/Tup1-type co-repressor TOPLESS (TPL) and its homologues through an EAR repression motif. Overexpression of NINJA reduces jasmonate sensitivity, while knock-down of NINJA leads to increased sensitivity. Microarray analysis reveals that NINJA KD plants overexpress many early jasmonate-responsive genes. These findings suggest that NINJA functions as a negative regulator of jasmonate signaling by connecting JAZ proteins to TPL co-repressors. The study also highlights the parallelism between auxin and jasmonate signaling pathways, where both involve the recruitment of co-repressors to complex formation.The study investigates the role of NINJA, a previously uncharacterized protein, in jasmonate signaling in plants. NINJA is shown to interact with JAZ proteins, which are repressors of gene expression in response to jasmonate. The interaction between NINJA and JAZ proteins is mediated by the TIFY motif of JAZ proteins and the C-terminal domain of NINJA. NINJA also interacts with the Groucho/Tup1-type co-repressor TOPLESS (TPL) and its homologues through an EAR repression motif. Overexpression of NINJA reduces jasmonate sensitivity, while knock-down of NINJA leads to increased sensitivity. Microarray analysis reveals that NINJA KD plants overexpress many early jasmonate-responsive genes. These findings suggest that NINJA functions as a negative regulator of jasmonate signaling by connecting JAZ proteins to TPL co-repressors. The study also highlights the parallelism between auxin and jasmonate signaling pathways, where both involve the recruitment of co-repressors to complex formation.