Molecular Mechanisms of Transcriptional Repression Specific to Plants

Dear Colleagues,

Recently, it has become evident that negative regulations play an important role in the control of various plant responses, which includes resistance to environmental stresses, hormone responses, vernalization, biological rythms, flowering, etc. For example, most phytohormones do not directly activate hormone-responsive genes but rather deactivate negative factors that suppress gene expression: Auxin assists degradation of the AUX/IAA transcriptional repressor; gibberellins promote degradation of DELLA that inhibits DNA binding of the PIF transcription factor; and brasinosteroid promotes stabilization of of BES1/BZR1 transcription factor by inhibiting its phosphorylation. Regarding developments, TCP transcription factors suppress meristem formation by restricting the area of expression of CUC genes; FT is repressed by FLC; miR172 promotes change from a vegetative to a reproductive phase; and endosperm development is suppressed through genome imprinting by the time of fertilization. These suggest that the plant genome contains a number of negative regulators, which maintain homeostasis under normal conditions by suppressing the genes that respond to environmental changes. Negative regulations are found in various stages through genome to post-transcriptional levels. Chromatin modifications, namely, DNA methylation and histone modification, repress transcription of the specific genes and also induce genome imprinting; transcriptional repressors repress transcription of their target genes; small RNAs degrade mRNA or induce DNA methylation; protein activities are suppressed through modification and degradation. Arabidopsis has around 2000 genes for transcription factors, and 15% of them contain a plant-specific EAR or EAR-like repression domain, implying that around 300 transcription factors act as transcriptional repressors in Arabidopsis. These suggest that transcriptional repression plays an important role as the negative regulator of gene expression in plants. The transcription factors that activate negative regulators, such as TCPs, are to be negative factors, and the transcriptional repressors that repress negative regulators, such as WUS, are positive regulators. However, the regulation mechanisms of the negative regulators or their function role on the gene expression have not been fully characterized.

This Special Issue is to address the functional roles of negative regulators by showing various physiological phenomena, regulated mainly by transcriptional repression in plants.

Prof. Masaru Ohme-Takagi
Dr. Hironori Takasaki
Guest Editors

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• transcription
• gene regulation
• repressor
• stress response
• flowering
• negative regulation
• epigenesis