RT Journal Article
SR Electronic
T1 Divergent receptor proteins confer responses to different karrikins in two ephemeral weeds
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 376939
DO 10.1101/376939
A1 Yueming Kelly Sun
A1 Adrian Scaffidi
A1 Jiaren Yao
A1 Kim Melville
A1 Steven M Smith
A1 Gavin R Flematti
A1 Mark T Waters
YR 2018
UL http://biorxiv.org/content/early/2018/07/25/376939.abstract
AB Seed germination is responsive to environmental chemical cues, such as karrikins, which are germination stimulants produced from wildfires1,2. Seeds of Brassica tournefortii – a widespread problematic weed associated with post-fire and disturbance sites – are highly sensitive to KAR1, the most abundant karrikin, whereas Arabidopsis thaliana responds more sensitively to KAR2, a less abundant karrikin3,4. The mechanism for these differential responses is unclear. KARRIKIN INSENSITIVE2 (KAI2), a paralogue of the strigolactone receptor DWARF14 (D14), is the putative karrikin receptor identified from Arabidopsis4,5. Here we show that B. tournefortii exhibits greater sensitivity for KAR1 relative to KAR2 in multiple biological assays. We demonstrate that B. tournefortii differentially expresses three KA12 homologues, two of which rescue the Arabidopsis kai2-2 null mutant. Notably, the most abundantly expressed homologue in B. tournefortii is sufficient to confer enhanced responses to KAR1 relative to KAR2 when expressed in Arabidopsis. We further identify two variant amino acid residues that support differential ligand preferences between the two B. tournefortii homologues. Our findings provide clear evidence that KAI2 is the receptor for karrikins, since specific amino acid substitutions near the active site change ligand specificity. Our results also suggest that duplication and diversification of KAI2 proteins could provide weedy ephemerals with the ability to respond sensitively to different karrikins or related compounds produced by environmental disturbance.