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An allelic series at the KARRIKIN INSENSITIVE  2 locus of Arabidopsis thaliana decouples ligand hydrolysis and receptor degradation from downstream signalling
Author(s) -
Yao Jiaren,
Mashiguchi Kiyoshi,
Scaffidi Adrian,
Akatsu Tomoki,
Melville Kim T.,
Morita Ryo,
Morimoto Yu,
Smith Steven M.,
Seto Yoshiya,
Flematti Gavin R.,
Yamaguchi Shinjiro,
Waters Mark T.
Publication year - 2018
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.14017
Subject(s) - strigolactone , butenolide , receptor , mutant , biology , arabidopsis , arabidopsis thaliana , biochemistry , ligand (biochemistry) , enzyme , microbiology and biotechnology , genetics , gene , botany
Summary Karrikins are butenolide compounds present in post‐fire environments that can stimulate seed germination in many species, including Arabidopsis thaliana . Plants also produce endogenous butenolide compounds that serve as hormones, namely strigolactones ( SL s). The receptor for karrikins ( KARRIKIN INSENSITIVE  2; KAI 2) and the receptor for SL s ( DWARF 14; D14) are homologous proteins that share many similarities. The mode of action of D14 as a dual enzyme receptor protein is well established, but the nature of KAI 2‐dependent signalling and its function as a receptor are not fully understood. To expand our knowledge of how KAI 2 operates, we screened ethyl methanesulphonate ( EMS )‐mutagenized populations of A. thaliana for mutants with kai2 ‐like phenotypes and isolated 13 new kai2 alleles. Among these alleles, kai2‐10 encoded a D184N protein variant that was stable in planta . Differential scanning fluorimetry assays indicated that the KAI 2 D184N protein could interact normally with bioactive ligands. We developed a KAI 2‐active version of the fluorescent strigolactone analogue Yoshimulactone Green to show that KAI 2 D184N exhibits normal rates of ligand hydrolysis. KAI 2 D184N degraded in response to treatment with exogenous ligands, suggesting that receptor degradation is a consequence of ligand binding and hydrolysis, but is insufficient for signalling activity. Remarkably, KAI 2 D184N degradation was hypersensitive to karrikins, but showed a normal response to strigolactone analogues, implying that these butenolides may interact differently with KAI 2. These results demonstrate that the enzymatic and signalling functions of KAI 2 can be decoupled, and provide important insights into the mechanistic events that underpin butenolide signalling in plants.

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