The LDL1/2-HDA6 histone modification complex interacts with TOC1 and regulates the core circadian clock components in Arabidopsis
Hung, F.Y., Chen, F.F., Li, C., Chen, C., Chen, J.H., Cui, Y., Wu, K. (2019). The LDL1/2-HDA6 histone modification complex interacts with TOC1 and regulates the core circadian clock components in Arabidopsis. Frontiers in Plant Science, [online] 10 http://dx.doi.org/10.3389/fpls.2019.00233
Plain language summary
The circadian rhythm is an endogenous oscillation widely observed in plants, animals, fungi and cyanobacteria. They are endogenously generated and self-sustaining; and are defined as the time to complete one cycle of 24 hours. The circadian clock central loop is a negative feedback loop composed of the core circadian clock components such as TOC1 and CCA1 and LHY. While CCA1 and LHY are highly expressed in the morning, TOC1 is expressed in the evening.
Histone, a protein found in the nucleus of most living cells, undergoes many modifications which play important roles in the regulation of gene expression. Some of the many important Histone modifications are histone methylation and histone deactylation (HDAC). Our study indicated that CCA1 can interact with HDAC complex to regulate gene expression of CCA1. We also demonstrated that HDAC complex can be recruited by CCA1 and LHY to their target genes including TOC1 gene. Furthermore, HDAC complex and TOC1 co-target a subset of genes involved in the circadian rhythm.
In Arabidopsis, the circadian rhythm is associated with multiple important biological processes and maintained by multiple interconnected loops that generate robust rhythms. The circadian clock central loop is a negative feedback loop composed of the core circadian clock components. TOC1 (TIMING OF CAB EXPRESSION 1) is highly expressed in the evening and negatively regulates the expression of CCA1 (CIRCADIAN CLOCK ASSOCIATED 1)/LHY (LATE ELONGATED HYPOCOTYL). CCA1/LHY also binds to the promoter of TOC1 and represses the TOC1 expression. Our recent research revealed that the histone modification complex comprising of LYSINE-SPECIFIC DEMETHYLASE 1 (LSD1)-LIKE 1/2 (LDL1/2) and HISTONE DEACETYLASE 6 (HDA6) can be recruited by CCA1/LHY to repress TOC1 expression. In this study, we found that HDA6, LDL1, and LDL2 can interact with TOC1, and the LDL1/2-HDA6 complex is associate with TOC1 to repress the CCA1/LHY expression. Furthermore, LDL1/2-HDA6 and TOC1 co-target a subset of genes involved in the circadian rhythm. Collectively, our results indicate that the LDL1/2-HDA6 histone modification complex is important for the regulation of the core circadian clock components.