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The Mg-Chelatase H Subunit of Arabidopsis Antagonizes a Group of Transcription Repressors to Relieve ABA-Responsive Genes of Inhibition
Yi Shanga,1, Lu Yana,b,1, Zhi-Qiang Liua,b,1, Zheng Caoa,b,1, Chao Meia,1, Qi Xina,b, Fu-Qing Wua,b, Xiao-Fang Wanga,b, Shu-Yuan Dua, Tao Jianga,b, Xiao-Feng Zhanga, Rui Zhaoa,b, Hai-Li Suna,b, Rui Liua,b, Yong-Tao Yua and Da-Peng Zhanga,2
a Protein Science Laboratory of the Ministry of Education, School of Life Sciences, Tsinghua University, Beijing 100084, China
b College of Biological Sciences, China Agricultural University, Beijing 100094, China
The phytohormone abscisic acid (ABA) plays a vital role in plant development and response to environmental challenges, but the complex networks of ABA signaling pathways are poorly understood. We previously reported that a chloroplast protein, the magnesium-protoporphyrin IX chelatase H subunit (CHLH/ABAR), functions as a receptor for ABA in Arabidopsis thaliana. Here, we report that ABAR spans the chloroplast envelope and that the cytosolic C terminus of ABAR interacts with a group of WRKY transcription factors (AD1A/WRKY40, AD1B/WRKY18, and AD1C/WRKY60) that function as negative regulators of ABA signaling in seed germination and postgermination growth. AD1A, a central negative regulator, inhibits expression of ABA-responsive genes, such as ABI5. In response to a high level of ABA signal that recruits AD1A from the nucleus to the cytosol and promotes ABAR–AD1A interaction, ABAR relieves the ABI5 gene of inhibition by repressing AD1A expression. These findings describe a unique ABA signaling pathway from the early signaling events to downstream gene expression.
