title: Evidence for Ancient Origins of Bowman-Birk Inhibitors fromSelaginella moellendorffii.
abstract: Bowman-Birk Inhibitors (BBIs) are a well-known family of plant protease inhibitors first described 70 years ago. BBIs are known only in the legume (Fabaceae) and cereal (Poaceae) families, but peptides that mimic their trypsin-inhibitory loops exist in sunflowers (Helianthus annuus) and frogs. The disparate biosynthetic origins and distant phylogenetic distribution implies these loops evolved independently, but their structural similarity suggests a common ancestor. Targeted bioinformatic searches for the BBI inhibitory loop discovered highly divergent BBI-like sequences in the seedless, vascular spikemossSelaginella moellendorffiiUsing de novo transcriptomics, we confirmed expression of five transcripts inS. moellendorffiiwhose encoded proteins share homology with BBI inhibitory loops. The most highly expressed,BBI3, encodes a protein that inhibits trypsin. We needed to mutate two lysine residues to abolish trypsin inhibition, suggesting BBI3's mechanism of double-headed inhibition is shared with BBIs from angiosperms. AsSelaginellabelongs to the lycopod plant lineage, which diverged ∼200 to 230 million years before the common ancestor of angiosperms, its BBI-like proteins imply there was a common ancestor for legume and cereal BBIs. Indeed, we discoveredBBIsequences in six angiosperm families outside the Fabaceae and Poaceae. These findings provide the evolutionary missing links between the well-known legume and cerealBBIgene families.
authors.affiliation: School of Molecular Sciences, The University of Western Australia, Crawley, Perth 6009, Australia.|The ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Crawley, Perth 6009, Australia.
authors.forename: Amy M
authors.initials: AM
authors.lastname: James
authors.affiliation: School of Molecular Sciences, The University of Western Australia, Crawley, Perth 6009, Australia.|The ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Crawley, Perth 6009, Australia.
authors.forename: Achala S
authors.initials: AS
authors.lastname: Jayasena
authors.affiliation: School of Molecular Sciences, The University of Western Australia, Crawley, Perth 6009, Australia.|The ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Crawley, Perth 6009, Australia.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Zhang
authors.affiliation: La Trobe University, School of Life Sciences, ARC Centre of Excellence in Plant Energy Biology, Melbourne 3086, Australia.
authors.forename: Oliver
authors.identifier: http://orcid.org/0000-0002-7671-6983
authors.initials: O
authors.lastname: Berkowitz
authors.affiliation: The ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Crawley, Perth 6009, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Secco
authors.affiliation: School of Molecular Sciences, The University of Western Australia, Crawley, Perth 6009, Australia.
authors.forename: Gavin J
authors.initials: GJ
authors.lastname: Knott
authors.affiliation: La Trobe University, School of Life Sciences, ARC Centre of Excellence in Plant Energy Biology, Melbourne 3086, Australia.
authors.forename: James
authors.initials: J
authors.lastname: Whelan
authors.affiliation: School of Molecular Sciences, The University of Western Australia, Crawley, Perth 6009, Australia.
authors.forename: Charles S
authors.identifier: http://orcid.org/0000-0002-9584-6783
authors.initials: CS
authors.lastname: Bond
authors.affiliation: School of Molecular Sciences, The University of Western Australia, Crawley, Perth 6009, Australia joshua.mylne@uwa.edu.au.|The ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, Crawley, Perth 6009, Australia.
authors.forename: Joshua S
authors.identifier: http://orcid.org/0000-0003-4957-6388
authors.initials: JS
authors.lastname: Mylne
mesh_terms: D019143:Evolution, Molecular; D007887:Fabaceae / Q000378:metabolism; D019684:Magnoliopsida / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D006109:Poaceae / Q000378:metabolism; D032503:Selaginellaceae / Q000378:metabolism*; D014361:Trypsin Inhibitors / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D014361:Trypsin Inhibitors