Bulking up: do plants make gains in secondary metabolites through genome duplication?

Whole genome duplication is often suggested as a major driver of developmental variation and complexity in plants. However, its effects can be variable with regard to particular traits. For example, whole genome duplications have been suggested to support greater resistance to herbivorous insects in some species, but to result in greater susceptibility to herbivory in other species. The effects of whole genome duplications may therefore vary trait-to-trait between species. Particularly associated with interactions with herbivores, as well as with pollinating insects, in plants are secondary metabolites.

Secondary metabolites are metabolites that are not strictly necessary for growth and development of plants, but fulfil other functions to promote successful survival and reproduction of plants. The effect of whole genome duplications on presence, absence and complexity of plant secondary metabolites is uncertain. To redress this imbalance, Gaynor, Lim-Hing and Mason from the University of Central Florida survey known datasets in their recent Annals of Botany paper to investigate whether there is a general trend in the effect of whole genome duplications on secondary metabolites in plants.

The authors first hypothesise that whole genome duplication events increase the overall concentration of secondary metabolites in plants. Based on 12 studies, the authors conclude that this is not the case. While some studies do associate higher ploidy (a proxy for the number of genome duplications) with higher concentrations of secondary metabolites, others show that low ploidy can also be associated with high concentrations of secondary metabolites. Moreover, other studies show no relationship between the two at all. Related to this, the authors also hypothesise that whole genome duplication events may be associated with relative concentration changes between specific groups of secondary metabolites. However, the authors also find no overall trends between concentrations of different secondary metabolite groups and high or low ploidy.

The third and final hypothesis that the authors present is that whole genome duplications may produce greater diversity of secondary metabolites. About half of the studies surveyed by Gaynor, Lim-Hing and Mason reported no pattern in secondary metabolite diversity that associated with ploidy status. The other half of the studies surveyed did record diversity changes associated with ploidy status. However, these again showed no robust overall trend – some studies recorded higher diversity of secondary metabolites with lower ploidy while some others recorded higher diversity with high ploidy.

This survey by Gaynor, Lim-Hing and Mason therefore indicates that whole genome duplications can have variable effects on concentration and diversity of plant secondary metabolites. Gaynor, Lim-Hing and Mason point out that to understand more about this variation in secondary metabolite production in different ploidy states, future work should ‘assess not only metabolomics, but integrate this information with dynamics at the scales of genomic architecture, gene expression, and the proteome, in particular enzyme function’. They also concede that the studies they survey do not necessarily align precisely in terms of techniques used or experimental set-ups to assess secondary metabolite relationships to ploidy. Further work is therefore needed, but this study highlights that whilst whole genome duplications may be broadly associated with increased developmental complexity, this does not necessarily apply to all plant traits.

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