A plant-centric view of class B flavin-dependent monooxygenase evolution and diversity

Flavin-dependent monooxygenases (FMOs) are ancient enzymes present throughout all kingdoms of life. FMOs utilize flavin-based cofactors to incorporate an oxygen atom into their substrate, altering its chemical properties. Class B FMOs are enriched throughout the plant kingdom, catalyzing essential reactions for plant development and defense, including auxin biosynthesis and systemic acquired resistance. Despite these essential metabolic roles, class B FMO functional characterization remains relatively limited, with no common evolutionary framework for FMO diversity across the plant kingdom currently available. By mining genomes representing 78 major Viridiplantae lineages, we present a curated dataset and comprehensive plant-centric phylogenetic analysis of class B FMOs, classifying eight distinct families: BVMO, N-Ox, N-Ox like 1, SeedlessFMO, S-Ox, S-Ox like 1, S-Ox like 2, and YUCCA. Most families evidently originate from an algal progenitor, although disparate degrees of FMO prevalence within and across families suggest multiple acquisition events in plants via horizontal gene transfer. Structural modeling and domain architecture analysis provide a refined framework for class B FMO diversity in plants delivering new insights into protein diversity and evolution. This plant-centric focus on class B FMOs provides an important resource that will facilitate further biochemical and functional characterization within plant development and response to environmental change.