Detection of Parasitic Plant Suicide Germination Compounds Using a High-Throughput Arabidopsis HTL/KAI2 Strigolactone Perception System

• HTL/KAI2 is a receptor for strigolactones, karrikins, and cotylimides
• HTL/KAI2 interacts with the ubiquitin ligase MAX2 in a ligand-dependent manner
• The HTL/KAI2-MAX2 interaction can be used to identify new strigolactone mimics
• Structurally diverse SL mimics stimulate parasitic plant germination

SummaryStrigolactones are terpenoid-based plant hormones that act as communication signals within a plant, between plants and fungi, and between parasitic plants and their hosts. Here we show that an active enantiomer form of the strigolactone GR24, the germination stimulant karrikin, and a number of structurally related small molecules called cotylimides all bind the HTL/KAI2 α/β hydrolase in Arabidopsis. Strigolactones and cotylimides also promoted an interaction between HTL/KAI2 and the F-box protein MAX2 in yeast. Identification of this chemically dependent protein-protein interaction prompted the development of a yeast-based, high-throughput chemical screen for potential strigolactone mimics. Of the 40 lead compounds identified, three were found to have in planta strigolactone activity using Arabidopsis-based assays. More importantly, these three compounds were all found to stimulate suicide germination of the obligate parasitic plant Striga hermonthica. These results suggest that screening strategies involving yeast/Arabidopsis models may be useful in combating parasitic plant infestations.

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