Correlation in plant volatile metabolites: physiochemical properties as a proxy for enzymatic pathways and an alternative metric of biosynthetic constraint

Abstract

From intra-individual regulation of metabolism to entire ecosystem functioning, the thousands of biogenic compounds produced by organisms serve as a major component of ecological and evolutionary diversity mediating interactions across scales. Earlier work considers canonical reactions, defined as reactions specified along accepted (experimentally validated or theoretically postulated) biosynthetic pathways, as the primary form of constraint on chemical diversity. An emerging understanding of non-canonical reactions (reactions which occur independently of canonical reactions) suggests that the physical chemistry of compounds may play a larger role in constraining chemo-diversity than previously thought. We selected 24 studies of plant volatile profiles, satisfying a defined set of criteria, to assess the extent of correlation among profiles attributable to either shared biosynthetic enzymes or physiochemical properties. Across studies, regardless of treatment, 0.17 (±?0.16 SD) adjusted R² was attributed to both shared biosynthetic enzymes and physiochemical properties; however, there were no significant differences between the amount of unique variance attributed to shared enzymes (0.05?±?0.08 SD) or physiochemical properties (0.03?±?0.06 SD). The amount of unique variance explained by physiochemical properties, independent of their canonical relationships, provides a metric for evaluating the role of non-enzymatic and non-canonical reactions in constraining molecular diversity.