2025-09-22 マックス・プランク研究所(MPG)
Web要約 の発言:
<関連情報>
- https://www.mpg.de/25436854/conifers-protect-themselves-against-bark-beetles-with-active-substances-from-two-eras
- https://www.pnas.org/doi/10.1073/pnas.2510962122
祖先的なジテルペン合成酵素における有利なエピスタシスが、針葉樹における樹脂酸前駆体の収斂進化を促進した Favorable epistasis in ancestral diterpene synthases promoted convergent evolution of a resin acid precursor in conifers
Andrew J. O’Donnell, Preston J. Pellatz, Caroline S. Nichols, +2 , and Axel Schmidt
Proceedings of the National Academy of Sciences Published:September 23, 2025
DOI:https://doi.org/10.1073/pnas.2510962122
Significance
The repeated evolution of a trait through different mutations in different species is called convergent evolution, but the causes of such repeatability are rarely understood. As an example of convergence, conifers from the related genera Picea, Abies, and Pinus each evolved pairs of enzymes that form identical products known as diterpenes. Using reconstructed ancestral enzymes that predate the convergence, we found that several alternative amino acid replacements in recent ancestors were responsible for driving identical gains in diterpene formation. However, analysis of these replacements in more ancient enzymes showed that there was a point in conifer history when diterpene evolution became especially repeatable. We found that a genetic mechanism, termed “epistasis,” led to this enhanced repeatability.
Abstract
A long-standing question in biology is what makes evolution more or less repeatable. Although evolution seems repeatable when observing convergent phenotypic outcomes, each episode of convergence could have been contingent on an idiosyncratic history that is not expected to repeat. Overlooking events that preceded convergent episodes therefore risks overestimating repeatability. Here, we demonstrate using resurrected ancestral proteins that the evolution of a characteristic diterpene resin acid precursor, isopimaradiene, became especially repeatable in conifers following genetic divergence that simultaneously changed the effects of phenotype-altering substitutions in diterpene synthase enzymes. We found that millions of years of epistatic change prior to three genus-level episodes of convergent isopimaradiene formation led to ancestral diterpene synthases in the family Pinaceae that served as suitable starting points for evolving identical products. However, enzymes predating the Pinaceae formed different diterpenes when the same substitutions were introduced as mutations, indicating that critical alterations in the effects of substitution occurred after the origin of this plant family. Because these alterations occurred prior to the evolution of isopimaradiene, the convergence appears dependent on a history that is less likely to repeat. Our work shows how contingency can lead to repeatable evolution of a trait in related present-day plant lineages.
