Maximum likelihood (ML) phylogeny of MA X2 orthologs from land plants. Sequences were obtained from GenBank (www.ncbi.nlm.nih.gov) and the Parasitic Plant Genome Project (ppgp.huck.psu.edu), using the Arabidopsis thaliana MA X2 amino acid sequence as a query. Full-length sequences were aligned using MA FFT (mafft.cbrc.jp/alignment/software/), and regions of poor alignment were removed manually with PFAAT.41 The phylogeny was constructed using RAxML BlackBox.42 The tree was rooted on a clade comprising Arabidopsis thaliana TIR1 and its orthologs. Numbers indicate branch support (100 bootstrap replicates). GenBank protein IDs for sequences used to generate the tree are: Arabidopsis thaliana, 18406017 (MA X2) and 254028670 (TIR1); Arabidopsis lyrata, 297824229; Thellungiella halophila, 312282253 and 312281471; Pisum sativum, 89329716; Ricinus communis, 255575295 and 255559322; Nicotiana tabacum, 254028670; Populus trichocarpa, 224128748; Vitis vinifera, 302143426; Oryza sativa cv. Japonica, 297724489; Sorghum bicolor, 242092018; Physcomitrella patens, 168039586 and 168062926; Selaginella moellendorffii, 302816439; and Picea sitchensis, 148906666. The Brachypodium distachyon sequence was derived from the locus identifier Bradi1g49120.1 (db.brachypodium.org). For Orobanche aegyptiaca, the protein sequence was derived from PPGP contig OrAe0GB1_43412. For Triphysaria versicolor and Striga hermonthica, sequences were assembled from multiple PPGP sequences to generate a contig that encoded a putative full-length protein.

Chemical structure of two bioactive karrikins, KAR₁ and KAR₂, and of the synthetic strigolactone GR24. Note that both classes of compounds have a butenolide ring in common (grey) which is required for activity.