A Feedforward Transcriptional Loop in Leaf Senescence
Zhuo et al. show the existence of jasmonate-activated MYC2-Dof2.1-MYC2 transcriptional loop that is involved in the promotion of leaf senescence in Arabidopsis. Plant Cell https://doi.org/10.1105/tpc.19.00297
By M. Zhuo, Y. Sakuraba, and S. Yanagisawa, The University of Tokyo, Japan
Background: Dof (DNA-binding with one finger) proteins are plant-specific transcription factors associated with a variety of physiological processes; however, it has not been shown that Dof proteins are involved in jasmonate (JA) responses. JA and its derivatives are lipid-derived phytohormones involved in a variety of plant processes, including leaf senescence, inhibition of root elongation, and responses to wounding and pathogen. In Arabidopsis, the bHLH transcription factor MYC2 is a central regulator of JA responses. Previous intensive studies revealed that post-translational regulation of MYC2 occupies a central position in the mechanism underlying JA signaling and responses: In the absence of JA, JASMONATE-ZIM-DOMAIN (JAZ) proteins form complexes with MYC2, the TOPLESS transcriptional co-repressor, and NOVEL INTERACTOR OF JAZ (NINJA) adaptor protein to inactivate MYC2. In the presence of JA, however, JAZ proteins interact with CORONATINE INSENSITIVE 1 (COI1), an F-box protein of the SCF E3 ubiquitin ligase complex, and then JAZ proteins are degraded by the 26S proteasome, leading to the release of MYC2 from JAZ containing-complexes.
Question: MYC2 expression is strongly induced by JA. Thus, the induction of MYC2 expression might be associated with JA responses. However, the biological significance and underlying molecular mechanism of this induction are not yet understood.
Findings: Disruption of Dof2.1, a JA-inducible gene, led to a marked reduction in promotion of leaf senescence and inhibition of root development, while overexpression of Dof2.1 promoted these processes, indicating that Dof2.1 functions as an enhancer of JA-induced leaf senescence. Furthermore, Dof2.1 enhanced JA-induced leaf senescence by directly activating the MYC2 promoter. MYC2 was also identified as a transcriptional activator responsible for JA-inducible expression of Dof2.1. Thus, Dof2.1 acts as an enhancer of JA-induced leaf senescence through a MYC2-Dof2.1-MYC2 feedforward transcriptional loop. This finding also indicates that a Dof protein is involved in JA responses.
Next steps: Although we revealed that Dof2.1 directly promotes MYC2 expression, other genes whose expression levels are directly regulated by Dof2.1 are yet to be identified. Thus, identification of other direct target genes of Dof2.1 may expand our understanding of the function of Dof2.1 in stress responses.
Mengna Zhuo, Yasuhito Sakuraba, Shuichi Yanagisawa (2019) A Jasmonate-activated MYC2-Dof2.1-MYC2 Transcriptional Loop Promotes Leaf Senescence in Arabidopsis. Plant Cell https://doi.org/10.1105/tpc.19.00297