Fig. 2: Cyanogenic glycoside content and FMO transcript abundances in tissues from the two modern fern species Pteridium aquilinum and Phlebodium aureum.

a Two phenylalanine-derived cyanogenic glycosides have been reported from ferns: the monoglucoside prunasin (D-mandelonitrile-β-D-glucopyranoside) and the diglycoside vicianin (6-O-arabinopyranosylglucopyranoside). b Phylogenetic relationship between Pteridium aquilinum (Dennstaedtiaceae) and Phlebodium aureum (Polypodiaceae) showing that these two modern ferns species diversified 140 million years ago (tree adapted from⁴³). c Content of vicianin across different tissue types of P. aureum (see also Supplementary Fig. 1), with the blue bars indicating the tissue selected for downstream transcriptomic analysis. d Content of prunasin in the pinnae of a population of 25 field-collected P. aquilinum, with the green bars indicating individuals selected for transcriptomic analysis. e Transcript abundance of predicted flavin monooxygenases (FMOs) in tissues of P. aquilinum and P. aureum containing high (gray bars) or low (black bars) cyanogenic glycoside levels. Arrows indicate candidate genes. TPM transcripts per million mapped reads. f Schematic illustration of identity and motifs in the transcriptome-deduced amino acid sequences of Paq18302 (PaqFOS1) and Pa22578. Differences between Pa22578 and the isolated PaFOS1 are indicated by blue lines. The position of putative binding motifs for FAD and NADPH, the FATGY and FMO-identifier motifs conserved across plant FMOs are highlighted. Supporting alignment is shown in Supplementary Fig. 1.