Arabidopsis ECAP is a New Adaptor Protein that Connects JAZ Repressors with TPR2 Co-repressor to Suppress Jasmonate-Responsive Anthocyanin Accumulation

Abstract Suppression mechanisms employed by transcriptional repressors commonly exist in diverse phytohormone signaling pathways. In Arabidopsis thaliana, JASMONATE-ZIM DOMAIN (JAZ) proteins are transcriptional repressors that function as negative regulators of diverse JA responses. Novel Interactor of JAZ (NINJA) is an adaptor protein connecting JAZs with the co-repressor, TOPLESS (TPL), to mediate gene repression in JA-dependent root growth inhibition and defense pathways. However, whether NINJA or other adaptor proteins are employed in other JA responsive biological processes remains to be elucidated. In the present study, we demonstrate that a previously uncharacterized protein, ECAP ( E AR motif- C ontaining A daptor P rotein), directly interacts with JAZ6/8 and enhances their transcriptional repression activities. We also provide evidence that ECAP is a novel adaptor protein for JAZ6/8 recruitment of the transcriptional co-repressor, TPR2, into a transcriptional repressor complex, to repress the WD-repeat/bHLH/MYB complex, an important transcriptional activator in the JA-dependent anthocyanin biosynthesis pathway. This novel insight, together with previous studies, reveals that specific adaptor proteins are critical for distinct JA responses by pairing different JAZs (which possess overlapping but also individual functions) with the general co-repressors, TPL and TPRs.