No abstract

Strigolactones are plant hormones and rhizosphere signalling molecules with key roles in plant development, mycorrhizal fungal symbioses, and plant parasitism. Currently, sensitive, specific, and high-throughput methods of detecting strigolactones are limited. Here, we developed genetically encoded fluorescent strigolactone biosensors based on the strigolactone receptors DAD2 from Petunia hybrida, and HTL7 from Striga hermonthica via domain insertion of circularly permuted GFP. The DAD2 biosensor exhibited loss of cpGFP fluorescence in vitro upon treatment with the strigolactones 5deoxystrigol and orobanchol, or the strigolactone analogue GR24. The biosensor likewise responded to strigolactones in an in vivo protoplast system, and retained strigolactone hydrolysis activity. The ShHTL7 biosensor exhibited loss of cpGFP fluorescence upon GR24 treatment in vitro, and responded to a specific inhibitor of ShHTL7 but not DAD2, indicating that the biosensors retained the specificity of their parent receptors. These biosensors have applications in high-throughput screening, and may also have utility for studying strigolactone biology.

The strigolactone (SL) class of phytohormones shows broad chemical diversity, the functional importance of which remains to be fully elucidated, along with the enzymes responsible for the diversification of the SL structure. Here we explore the functional evolution of the highly conserved CYP711A P450 family, members of which catalyze several key monooxygenation reactions in the strigolactone pathway.Ancestral sequence reconstruction was utilized to infer ancestral CYP711A sequences based on a comprehensive set of extant CYP711 sequences. Eleven ancestral enzymes, corresponding to key points in the CYP711A phylogenetic tree, were resurrected and their activity was characterized towards the native substrate carlactone and the pure enantiomers of the synthetic strigolactone analogue, GR24.The ancestral and extant CYP711As tested accepted GR24 as a substrate and catalyzed several diversifying oxidation reactions on the structure. Evidence was obtained for functional divergence in the CYP711A family. The monocot group 3 ancestor, arising from gene duplication events within monocot grasses, showed both increased catalytic activity towards GR24 and high stereoselectivity towards the GR24 isomer resembling strigol-type SLs.These results are consistent with a role for CYP711As in strigolactone diversification in early land plants, which may have extended to the diversification of strigol-type SLs.