Zinc finger of Arabidopsis thaliana 6 is involved in melatonin‐mediated auxin signaling through interacting INDETERMINATE DOMAIN15 and INDOLE‐3‐ACETIC ACID 17

Abstract Although accumulating evidence demonstrates the cross talk between melatonin and auxin as derivatives of tryptophan, the underlying signaling events remain unclear. In this study, we found that melatonin and auxin mediated the transcriptional levels of zinc finger of Arabidopsis thaliana ( ZAT 6 ) in a mutually antagonistic manner. ZAT 6 negatively modulated the endogenous auxin level, and ZAT 6 knockdown plants were less sensitive to melatonin‐regulated auxin biosynthesis, indicating its involvement in melatonin‐mediated auxin accumulation. Additionally, the identification of INDETERMINATE DOMAIN 15 ( IDD 15) and INDOLE ‐3‐ ACETIC ACID 17 ( IAA 17) in Arabidopsis that interacted with ZAT 6 in vivo provided new insight of ZAT 6 ‐mediated auxin signaling. Further investigation showed that ZAT 6 repressed the transcription activation of IDD 15 on the YUC 2 promoter, while ZAT 6 inhibited the interaction of TRANSPORT INHIBITOR RESPONSE 1 ( TIR 1) and IAA 17 through competitively binding to IAA 17. Thus, both auxin synthesis and the auxin response were negatively modulated by ZAT 6 . Taken together, ZAT 6 is involved in melatonin‐mediated auxin signaling through forming an interacting complex of auxin signaling pathway in Arabidopsis .