Antagonistic HLH/bHLH transcription factors mediate brassinosteroid regulation of cell elongation and plant development in rice and Arabidopsis.
In rice (Oryza sativa), brassinosteroids (BRs) induce cell elongation at the adaxial side of the lamina joint to promote leaf bending. We identified a rice mutant (ili1-D) showing an increased lamina inclination phenotype similar to that caused by BR treatment. The ili1-D mutant overexpresses an HLH protein homologous to Arabidopsis thaliana Paclobutrazol Resistance1 (PRE1) and the human Inhibitor of DNA binding proteins. Overexpression and RNA interference suppression of ILI1 increase and reduce, respectively, rice laminar inclination, confirming a positive role of ILI1 in leaf bending. ILI1 and PRE1 interact with basic helix-loop-helix (bHLH) protein IBH1 (ILI1 binding bHLH), whose overexpression causes erect leaf in rice and dwarfism in Arabidopsis. Overexpression of ILI1 or PRE1 increases cell elongation and suppresses dwarf phenotypes caused by overexpression of IBH1 in Arabidopsis. Thus, ILI1 and PRE1 may inactivate inhibitory bHLH transcription factors through heterodimerization. BR increases the RNA levels of ILI1 and PRE1 but represses IBH1 through the transcription factor BZR1. The spatial and temporal expression patterns support roles of ILI1 in laminar joint bending and PRE1/At IBH1 in the transition from growth of young organs to growth arrest. These results demonstrate a conserved mechanism of BR regulation of plant development through a pair of antagonizing HLH/bHLH transcription factors that act downstream of BZR1 in Arabidopsis and rice.
Zhang
Li-Ying
LY
Key Laboratory of Photosynthesis and Environmental Molecular Biology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
Bai
Ming-Yi
MY
Wu
Jinxia
J
Zhu
Jia-Ying
JY
Wang
Hao
H
Zhang
Zhiguo
Z
Wang
Wenfei
W
Sun
Yu
Y
Zhao
Jun
J
Sun
Xuehui
X
Yang
Hongjuan
H
Xu
Yunyuan
Y
Kim
Soo-Hwan
SH
Fujioka
Shozo
S
Lin
Wen-Hui
WH
Chong
Kang
K
Lu
Tiegang
T
Wang
Zhi-Yong
ZY
D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D049108:Cell Enlargement; D004268:DNA-Binding Proteins; D018506:Gene Expression Regulation, Plant; D008855:Microscopy, Electron, Scanning; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D012275:Oryza / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D036226:Seedlings / Q000254:growth & development / Q000648:ultrastructure; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D013256:Steroids / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D018749:RNA, Plant; D013256:Steroids; D014157:Transcription Factors; C454444:BZR1 protein, Arabidopsis; C582892:IBH1 protein, Arabidopsis; C513126:PRE1 protein, Arabidopsis