Desmethyl butenolides are optimal ligands for karrikin receptor proteins

Abstract

Strigolactones and karrikins are butenolide molecules that regulate plant growth. They are perceived by the a/b-hydrolase DWARF14 (D14) and its homologue KARRIKIN INSENSITIVE2 (KAI2), respectively. Plant-derived strigolactones have a butenolide ring with a methyl group that is essential for bioactivity. By contrast, karrikins are abiotic in origin, and the butenolide methyl group is nonessential. KAI2 is probably a receptor for an endogenous butenolide, but the identity of this compound remains unknown. Here we characterise the specificity of KAI2 towards differing butenolide ligands using genetic and biochemical approaches. We find that KAI2 proteins from multiple species are most sensitive to desmethyl butenolides that lack a methyl group. Desmethyl-GR24 and desmethyl-CN-debranone are active by KAI2 but not D14. They are more potent KAI2 agonists compared with their methyl-substituted reference compounds both in vitro and in plants. The preference of KAI2 for desmethyl butenolides is conserved in Selaginella moellendorffii and Marchantia polymorpha, suggesting that it is an ancient trait in land plant evolution. Our findings provide insight into the mechanistic basis for differential ligand perception by KAI2 and D14, and support the view that the endogenous substrates for KAI2 and D14 have distinct chemical structures and biosynthetic origins.

The Physcomitrium (Physcomitrella) patens PpKAI2L receptors for strigolactones and related compounds function via MAX2-dependent and -independent pathways

“…Recent biochemistry experiments (Bürger et al 2019) showed that some PpKAI2L proteins could bind to KAR1 (PpKAI2L-H, K and L), while a previous study concluded that P. patens was insensitive to KAR1 (Hoffmann et al 2014). In the present work, we tested the KAR2 molecule, described as being more active than KAR1 in Arabidopsis (Waters et al 2015a;Yao et al 2021) (Figure 2A-B). KAR2 has an unmethylated butenolide group, unlike KAR1.…”

“…This conclusion also suggests that P. patens KL may be quite different from that of angiosperms. Recently, desmethyl butenolides were reported to be more potent and to function as specific ligands for KAI2, both in vitro and in plants, including the lycophyte Selaginella moellendorffii (S. moellendorffii) and the bryophyte Marchantia polymorpha (M. polymorpha) (Yao et al 2021). Thus, testing desmethyl butenolides, and in particular the (-)-desmethyl GR24 enantiomer (dGR24 ent5DS ) on P. patens plants and proteins is a priority in the search for a KL mimic.…”

ThePhyscomitrium (Physcomitrella) patensPpKAI2L receptors for strigolactones and related compounds highlight MAX2 dependent and independent pathways

“…Indeed, no transcriptional (PpCCD7 expression) or phenotypic response (caulonema length in the dark) to KAR1 was observed in either WT or the Ppccd8 mutant (Hoffmann et al 2014). In the present work, we tested the KAR2 molecule, described as being more active than KAR1 in Arabidopsis (Waters et al 2015;Yao et al 2021) ( Figure 2A-B). KAR2 has an unmethylated butenolide group, unlike KAR1.…”

Biological Functions of Strigolactones and Their Crosstalk With Other Phytohormones

“…The complex structure and stereochemistry of natural SLs limit their chemical synthesis. GR24, a synthetic SL analogue widely used in SL studies, is a racemic mixture of two 5-deoxystrigol (5DS)-configured enantiomers, namely, GR24 5DS and GR24 ent–5DS ( Yao et al, 2021 ).…”