The magnesium-chelatase H subunit binds abscisic acid and functions in abscisic acid signaling: new evidence in Arabidopsis.
Using a newly developed abscisic acid (ABA)-affinity chromatography technique, we showed that the magnesium-chelatase H subunit ABAR/CHLH (for putative abscisic acid receptor/chelatase H subunit) specifically binds ABA through the C-terminal half but not the N-terminal half. A set of potential agonists/antagonists to ABA, including 2-trans,4-trans-ABA, gibberellin, cytokinin-like regulator 6-benzylaminopurine, auxin indole-3-acetic acid, auxin-like substance naphthalene acetic acid, and jasmonic acid methyl ester, did not bind ABAR/CHLH. A C-terminal C370 truncated ABAR with 369 amino acid residues (631-999) was shown to bind ABA, which may be a core of the ABA-binding domain in the C-terminal half. Consistently, expression of the ABAR/CHLH C-terminal half truncated proteins fused with green fluorescent protein (GFP) in wild-type plants conferred ABA hypersensitivity in all major ABA responses, including seed germination, postgermination growth, and stomatal movement, and the expression of the same truncated proteins fused with GFP in an ABA-insensitive cch mutant of the ABAR/CHLH gene restored the ABA sensitivity of the mutant in all of the ABA responses. However, the effect of expression of the ABAR N-terminal half fused with GFP in the wild-type plants was limited to seedling growth, and the restoring effect of the ABA sensitivity of the cch mutant was limited to seed germination. In addition, we identified two new mutant alleles of ABAR/CHLH from the mutant pool in the Arabidopsis Biological Resource Center via Arabidopsis (Arabidopsis thaliana) Targeting-Induced Local Lesions in Genomes. The abar-2 mutant has a point mutation resulting in the N-terminal Leu-348-->Phe, and the abar-3 mutant has a point mutation resulting in the N-terminal Ser-183-->Phe. The two mutants show altered ABA-related phenotypes in seed germination and postgermination growth but not in stomatal movement. These findings support the idea that ABAR/CHLH is an ABA receptor and reveal that the C-terminal half of ABAR/CHLH plays a central role in ABA signaling, which is consistent with its ABA-binding ability, but the N-terminal half is also functionally required, likely through a regulatory action on the C-terminal half.
Wu
Fu-Qing
FQ
State Key Laboratory of Plant Physiology and Biochemistry , China Agricultural University, Beijing 100094, China.
Xin
Qi
Q
Cao
Zheng
Z
Liu
Zhi-Qiang
ZQ
Du
Shu-Yuan
SY
Mei
Chao
C
Zhao
Chen-Xi
CX
Wang
Xiao-Fang
XF
Shang
Yi
Y
Jiang
Tao
T
Zhang
Xiao-Feng
XF
Yan
Lu
L
Zhao
Rui
R
Cui
Zi-Ning
ZN
Liu
Rui
R
Sun
Hai-Li
HL
Yang
Xin-Ling
XL
Su
Zhen
Z
Zhang
Da-Peng
DP
D000040:Abscisic Acid / Q000378:metabolism* / Q000494:pharmacology; D000483:Alleles; D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D002846:Chromatography, Affinity; D018076:DNA, Complementary / Q000235:genetics; D018525:Germination / Q000187:drug effects; D008190:Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D030821:Plants, Genetically Modified; D011485:Protein Binding / Q000187:drug effects; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D036226:Seedlings / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development; D015398:Signal Transduction / Q000187:drug effects
D018076:DNA, Complementary; D021122:Protein Subunits; D000040:Abscisic Acid; D008190:Lyases; C086788:magnesium chelatase