The Mg-Chelatase H Subunit of Arabidopsis Antagonizes a Group of WRKY Transcription Repressors to Relieve ABA-Responsive Genes of Inhibition[W][OA]

Yi Shang,Lu Yan,Zhi-Qiang Liu,Zheng Cao,Chao Mei,Qi Xin,Fu-qing Wu,Xiao-fang Wang,Shu-Yuan Du,Tao Jiang,Xiao-Feng Zhang,Rui Zhao,Hai-Li Sun,Rui Liu,Yongtao Yu,Da-Peng Zhang

Published 2010 in The Plant Cell

ABSTRACT

This work identifies a group of WRKY transcription factors that function as negative abscisic acid (ABA) signaling regulators acting as transcription repressors directly downstream of a previously identified ABA receptor ABAR, describing an ABA signaling pathway from primary events to downstream gene expression. 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 (WRKY40, WRKY18, and WRKY60) that function as negative regulators of ABA signaling in seed germination and postgermination growth. WRKY40, a central negative regulator, inhibits expression of ABA-responsive genes, such as ABI5. In response to a high level of ABA signal that recruits WRKY40 from the nucleus to the cytosol and promotes ABAR–WRKY40 interaction, ABAR relieves the ABI5 gene of inhibition by repressing WRKY40 expression. These findings describe a unique ABA signaling pathway from the early signaling events to downstream gene expression.

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