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 (ZAT6) in a mutually antagonistic manner. ZAT6 negatively modulated the endogenous auxin level, and ZAT6 knockdown plants were less sensitive to melatonin-regulated auxin biosynthesis, indicating its involvement in melatonin-mediated auxin accumulation. Additionally, the identification of INDETERMINATE DOMAIN15 (IDD15) and INDOLE-3-ACETIC ACID 17 (IAA17) in Arabidopsis that interacted with ZAT6 in vivo provided new insight of ZAT6-mediated auxin signaling. Further investigation showed that ZAT6 repressed the transcription activation of IDD15 on the YUC2 promoter, while ZAT6 inhibited the interaction of TRANSPORT INHIBITOR RESPONSE 1 (TIR1) and IAA17 through competitively binding to IAA17. Thus, both auxin synthesis and the auxin response were negatively modulated by ZAT6. Taken together, ZAT6 is involved in melatonin-mediated auxin signaling through forming an interacting complex of auxin signaling pathway in Arabidopsis.

Melatonin‐deficient rice plants show a common semidwarf phenotype either dependent or independent of brassinosteroid biosynthesis

“…Several studies have reported possible altered IAA levels in response to melatonin treatment or by melatonin‐rich transgenic plants . To investigate the possible relationship between melatonin and IAA, we measured IAA levels in the melatonin‐deficient rice plants using an ELISA.…”

“…Melatonin is essential for normal growth and development, such as stomatal closure, the auxin signaling pathway, starch synthesis, plant regeneration, and root formation, as well as for defense against an array of biotic and abiotic stressors, including high light, pathogens, salt, senescence, and high temperature, among others . The functional roles of melatonin in plants are associated with crosstalk with plant hormones, such as auxin, cytokinin, salicylic acid, and abscisic acid …”

Direct comparison of Arabidopsis gene expression reveals different responses to melatonin versus auxin

“…It is known that endogenous auxin (IAA) levels are reduced by melatonin (1, 50, 100 and 200 μM) when supplemented in the growth medium in Arabidopsis by enhancing expression of Zinc Finger transcription factor ZAT6 [72]. Interestingly in the same study, ZAT6 showed no direct binding to TACAAT motifs in the promoter of the auxin biosynthetic gene YUC2 as analysed by ChIP-PCR.…”

Role of the INDETERMINATE DOMAIN Genes in Plants

“…The IDD proteins directly bind to the promoter regions of TAA1 , PIN1 , and YUC5 and activate their expression. IDD -regulated auxin signaling might be further regulated by ZAT6 [68]. Further study of crosstalk between hormone metabolism and the surrounding environment will lead to a better understanding of the role of IDD proteins in the regulation of hormonal signaling.…”