The strategic logic behind the approach is what makes it compelling. Rather than surveying genomes uniformly across the plant tree of life, the researchers concentrated their sampling on lineages that sit immediately on either side of key evolutionary forks in grass history. This technique, sometimes described as phylogenetic bracketing, allows investigators to infer the timing of a biochemical innovation by asking a simple comparative question: which organisms on one side of the branch possess the pathway, and which on the other side lack it? If a complete set of pathway genes appears in every descendant of one branch but in none of the closest relatives on the other, the origin of that pathway can be placed, with considerable confidence, in the interval between the two divergence events.

Applied to grasses, this logic yielded a dated origin for distinct starch metabolism. Starch is the dominant storage carbohydrate in plants and the principal caloric source for humanity, yet not all starch is built the same way. Grasses, which include the cereal crops that feed the bulk of the world’s population, assemble their storage and transitory starch with a characteristic suite of enzymes that differs in its composition and regulation from the starch systems of many other flowering plants. By mapping the presence of these enzyme sets onto the grass phylogeny, the study could show that the distinctive grass starch pathway arose in the ancestor of a specific branch of the grass family tree, and not earlier. The innovation, in other words, is not an ancient inheritance from the first flowering plants but a later acquisition that coincided with the diversification of the lineage that would eventually give rise to wheat, rice, maize, and their relatives.

The second gateway the study illuminated concerns lignin, the phenolic polymer that stiffens plant cell walls and enabled land plants to stand upright, conduct water under tension, and colonize dry terrestrial environments. Lignin is the product of the phenylpropanoid pathway, a metabolic assembly line that begins with the deamination of the aromatic amino acid phenylalanine by the enzyme phenylalanine ammonia lyase, universally abbreviated PAL. This reaction strips the amino group from phenylalanine and commits the carbon skeleton to the phenylpropanoid pipeline, from which lignin monomers, flavonoids, and thousands of specialized metabolites flow. PAL is therefore the gatekeeper of the entire pathway, the enzyme whose substrate preference determines which amino acids can enter the aromatic metabolism of the cell.

Here the study made its most mechanistically striking discovery. The genomic neighbourhood of ancestral PAL duplicates, examined across the sampled grass lineages, revealed that the PAL gene family had undergone duplication events whose timing could be anchored to the same phylogenetic framework used for the starch analysis. Duplicate genes are the raw material of metabolic evolution, because one copy can preserve the original function while the other accumulates mutations and explores new chemistry. But whether a duplicate actually acquires a new function depends on the specific amino acid changes that alter the shape and chemistry of the enzyme’s active site, and demonstrating this requires more than sequence comparison alone.

To close that gap, the researchers combined their genomic survey with structural and biochemical analysis of the ancestral and derived PAL enzymes. Structural modelling of the enzyme, informed by known PAL architectures, identified candidate positions where substitutions could plausibly change substrate handling. Biochemical characterization of the reconstructed enzymes then tested those predictions directly, measuring what each enzyme version could and could not do. The result was remarkably clean: two amino acid substitutions were sufficient to convert the substrate preference of the enzyme, opening a route by which tyrosine, rather than exclusively phenylalanine, could feed into phenylpropanoid metabolism.

This finding matters because the two aromatic amino acids are not interchangeable feedstocks. Phenylalanine and tyrosine sit at adjacent positions in the aromatic amino acid biosynthetic pathway, but they carry different side chains, and an ammonia lyase that accepts tyrosine produces a different immediate product, one that can be channeled toward particular classes of phenolic compounds. A tyrosine route into phenylpropanoid metabolism therefore represents a genuine expansion of the metabolic gateway, a new door into the pathway that did not exist in ancestors whose PAL enzymes were restricted to phenylalanine. In grasses, this expanded access has implications for the composition of lignin itself, since grass lignins are notable for incorporating substantial quantities of phenolic constituents derived through routes that other plants use only sparingly.

The evolutionary narrative that emerges from combining these strands is one of coordinated innovation. At a decisive branchpoint in grass ancestry, the lineage did not merely accumulate random sequence drift. It acquired a new starch metabolism with its own enzyme configuration, and it acquired an expanded aromatic gateway through PAL duplication and functional divergence. Both innovations would have reshaped the physiology of the plants that carried them. A distinctive starch metabolism alters how carbon is stored and mobilized across the day-night cycle and during development, while an enlarged phenylpropanoid input changes the raw material available for cell wall reinforcement and chemical defense. Together, these changes could have contributed to the ecological success of the grass lineage, which today covers roughly a third of the terrestrial land surface and supplies the majority of human caloric intake.

Methodologically, the study exemplifies a broader shift in how evolutionary metabolism is investigated. The classical approach, exemplified by landmark work on benzoxazinoid biosynthesis in grasses and by decades of comparative enzymology, identified pathways one at a time through careful biochemistry. The new approach inverts the logic: it starts from a well-resolved phylogeny, samples genomes strategically at branchpoints, identifies gene families whose duplication history coincides with metabolic transitions, and then moves into the laboratory to reconstruct and test the ancestral enzymes. Each step constrains the others. Phylogeny tells biochemistry where to look, and biochemistry confirms or refutes what the phylogeny suggests. The identification of two substitutions that opened the tyrosine route is a case study in how this iterative loop can convert a comparative pattern into a causal molecular mechanism.

The implications extend beyond evolutionary theory. Knowing when and how grasses acquired their distinctive starch and lignin systems provides a rational framework for crop improvement, because it identifies the enzymes and substitutions that define the grass-specific versions of these pathways. Engineers seeking to modify lignin for more efficient biofuel production, or to alter starch quality for food and industrial uses, can now consult an evolutionary record that indicates which enzyme versions are ancestral, which are derived, and which specific amino acid changes produced new functions. The branchpoints of grass evolution, once visible only as splits in a species tree, have thus become annotated waypoints on a metabolic map, marking the precise moments when the gateways of plant chemistry were opened, and pointing the way toward deliberate redesign of the pathways that feed and shelter the modern world.

Subject of Research: Evolutionary origins of grass starch and lignin metabolic pathways revealed through phylogenetic genome sampling and ancestral phenylalanine ammonia lyase enzyme analysis

Article Title: Branchpoints reveal metabolic gateways

Article References: Harding, E. A., Fernie, A. R., & Bulut, M. (2026). Branchpoints reveal metabolic gateways. Nature Plants. https://doi.org/10.1038/s41477-026-02434-1

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02434-1

Keywords: grass evolution, starch metabolism, lignin, phenylpropanoid pathway, phenylalanine ammonia lyase, gene duplication, tyrosine, phylogenetic bracketing, plant metabolism, genome evolution, ancestral enzyme reconstruction, cell wall biosynthesis

Grasses include wheat, rice, maize, barley and many other cereal crops that together provide a major share of the calories consumed worldwide. Their evolutionary success is striking because grasses can grow rapidly while producing substantial amounts of lignin, a complex structural polymer that strengthens plant tissues. Lignin is abundant in wood and other slow-growing plants, where it reinforces cell walls but can also make tissues more difficult to digest and process. Grasses appear to have combined strong structural support with unusually efficient growth, and the new research suggests that duplicated or alternative biochemical routes played a central role.

The study was led by researchers at the University of Wisconsin–Madison in collaboration with scientists from institutions including the University of Georgia and research organizations in the United Kingdom and Japan. The team focused on the metabolic pathways plants use to synthesize starch and lignin. Starch is a glucose-based storage molecule that accumulates in seeds and other tissues, providing energy for germination and early development. Lignin, by contrast, is deposited in cell walls, where it provides rigidity and helps plants transport water and remain upright. Both compounds are produced through networks of enzymes encoded by multiple genes, making their evolutionary history possible to reconstruct through comparative genomics.

To identify what changed during the emergence of grasses, the researchers examined the genome of Joinvillea ascendens, a long-leaved plant found in wet forests on South Pacific islands. Joinvillea belongs to a group that is closely related to grasses but diverged from the grass lineage before modern grasses appeared. It grows more slowly than many grasses and lacks the agricultural importance of cereal crops, but its evolutionary position makes it a valuable comparison. The researchers also sequenced the genomes of three related species, creating a broader genetic framework for distinguishing traits that evolved within grasses from those that were already present in their relatives.

Obtaining the plant material was itself a lengthy process. More than 100 seeds collected through the National Tropical Botanical Garden in Hawaii were initially available, but only two germinated. The plants then required approximately two years of growth before they were large enough to harvest for genomic analysis. Once DNA was obtained, the researchers compared thousands of genes and reconstructed the presence and history of biochemical pathways across the plant lineages. This approach allowed them to ask not only which genes exist in grasses, but also when particular genetic changes first appeared.

The starch results revealed a major difference between Joinvillea and grasses. The non-grass relative possesses a single pathway for starch synthesis, whereas all examined grasses contain two. The additional route appears to have originated in the common ancestor of grasses, creating what the researchers describe as a metabolic bypass. In biochemical terms, a bypass can provide an alternative route to the same end product, reducing dependence on a single sequence of reactions and potentially increasing the overall flow of carbon into starch. The researchers propose that this innovation may have substantially increased the capacity of grasses to store energy in seeds and developing tissues.

That advantage could have been especially powerful in open habitats, where sunlight is abundant but competition is intense. A seed with a larger or more rapidly accessible energy reserve can germinate, establish roots and produce leaves before neighboring plants become fully developed. Once photosynthesis begins, the young plant can generate additional sugars while continuing to grow upward toward the light. Over generations, even a modest improvement in early growth could produce a major evolutionary advantage. In agriculture, the same mechanism may have become highly valuable because humans selected grasses that efficiently channel carbon into energy-rich grains.

The researchers found a different evolutionary pattern in lignin production. Both grasses and Joinvillea possess two routes for synthesizing lignin, indicating that this dual-pathway system arose before the grass family itself evolved. The discovery challenges the assumption that every distinctive grass trait originated after grasses became recognizable as a separate group. Instead, some of the biochemical groundwork may have been laid in an ancient ancestor shared by grasses and their close relatives. The team then traced how the second lignin route was created and identified two DNA mutations that were critical and sufficient to establish the new pathway in the system they studied.

These mutations appear to have altered the behavior of enzymes involved in lignin biosynthesis, allowing plant metabolism to reach the same structural products through an alternative sequence of reactions. Such changes can increase flexibility and resilience by distributing biochemical work across more than one route. For plants, that may support rapid construction of stems and leaves without sacrificing the mechanical strength provided by lignin. The researchers say the findings could eventually guide efforts to engineer crops with improved biomass production, stronger stems or altered lignin composition. Introducing a second lignin route into other plants, however, would require careful testing because lignin affects growth, water transport, digestibility and the processing of plant material for biofuels.

The study’s broader message is that evolutionary success can depend on changes that are invisible to the eye but transformative at the molecular level. Grasses did not simply become dominant because they grew quickly; they may have inherited a biochemical architecture that allowed them to produce stored energy and structural material with exceptional efficiency. Understanding that architecture could help scientists improve cereal crops, increase nutritional yields and develop better bioenergy plants while reducing pressure on land and other resources. The researchers are now using this evolutionary knowledge as a foundation for plant biotechnology, exploring whether metabolic bypasses can be adapted to produce more useful nutrients, stronger biomass and valuable chemicals in agricultural species.

Subject of Research: Comparative genomics and the evolution of starch and lignin biosynthesis in grasses and their close relatives.

Article Title: Genomes of Poaceae sisters reveal key metabolic innovations preceding the evolution of grasses

News Publication Date: 20-Aug-2026

Web References: https://doi.org/10.1126/science.adv0443

References: Science, DOI: 10.1126/science.adv0443

Image Credits: Sarah Friedrich / UW–Madison

Keywords: grasses, cereal crops, plant evolution, comparative genomics, Joinvillea, starch biosynthesis, lignin biosynthesis, metabolic pathways, plant biotechnology, agriculture, bioenergy crops, evolutionary biology