title: Reporter Gene-Facilitated Detection of Compounds inArabidopsisLeaf Extracts that Activate the Karrikin Signaling Pathway.
abstract: Karrikins are potent germination stimulants generated by the combustion of plant matter. Treatment ofArabidopsiswith karrikins triggers a signaling process that is dependent upon a putative receptor protein KARRIKIN INSENSITIVE 2 (KAI2). KAI2 is a homolog of DWARF 14 (D14), the receptor for endogenous strigolactone hormones. Genetic analyses suggest that KAI2 also perceives endogenous signal(s) that are not strigolactones. Activation of KAI2 by addition of karrikins toArabidopsisplants induces expression of transcripts includingD14-LIKE 2(DLK2). We constructed the synthetic reporter geneDLK2:LUCinArabidopsis, which comprises the firefly luciferase gene (LUC) driven by theDLK2promoter. Here we describe a luminescence-based reporter assay withArabidopsisseeds to detect chemical signals that can activate the KAI2 signaling pathway. We demonstrate that theDLK2:LUCassay can selectively and sensitively detect karrikins and a functionally similar synthetic strigolactone analog. Crucially we show that crude extracts fromArabidopsisleaves can also activateDLK2:LUCin a KAI2-dependent manner. Our work provides the first direct evidence for the existence of endogenous chemical signals that can activate the KAI2-mediated signaling pathway inArabidopsis. This sensitive reporter system can now be used for the bioassay-guided purification and identification of putative endogenous KAI2 ligands or their precursors, and endogenous compounds that might modulate the KAI2 signaling pathway.
authors.affiliation: Australian Research Council Centre of Excellence in Plant Energy Biology, The University of Western Australia, Perth WA, Australia.
authors.forename: Yueming K
authors.initials: YK
authors.lastname: Sun
authors.affiliation: School of Chemistry and Biochemistry, The University of Western Australia, Perth WA, Australia.
authors.forename: Gavin R
authors.initials: GR
authors.lastname: Flematti
authors.affiliation: School of Biological Sciences, University of Tasmania, HobartTAS, Australia; Institute of Genetics and Developmental Biology, Chinese Academy of SciencesBeijing, China.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Smith
authors.affiliation: Australian Research Council Centre of Excellence in Plant Energy Biology, The University of Western Australia, PerthWA, Australia; School of Chemistry and Biochemistry, The University of Western Australia, PerthWA, Australia.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Waters
keywords: Arabidopsis; chemical biology; germination; karrikin; plant hormone; reporters; strigolactone