Why unseen grass fungal endophytes quietly shape plant chemistry

A shared chemical kitchen

Every blade of grass contains a hidden factory. Inside the leaves of warm-climate C4 grasses, unseen fungi live within plant cells without causing disease. These leaf-dwelling guests are known as foliar grass fungal endophytes.

Scientists wanted to know what controls the full suite of small compounds, called the metabolome, inside these plants. For a long time, experts expected a plant's family tree to dictate its chemistry. However, many wild grasses do not inherit their fungal partners through seeds. Instead, they catch these fungal roommates from the surrounding air through horizontal transmission. To see how these airborne visitors alter leaf makeup, scientists sampled wild grasses growing side by side.

Mapping the ingredients

The team collected 12 wild C4 grass species that grew together in the same natural space. These species had varied family roots and invasion backgrounds. Next, the team measured every small compound in the leaves. They found 1,723 distinct compounds in total, averaging 656 per plant species. They also catalogued the fungi living inside the leaves using culture dishes and direct DNA tests. This method captured both slow-growing species and types that cannot grow in dishes alone. In total, they found 127 cultured types and 388 culture-free groups, known as operational taxonomic units (OTUs).

By comparing the data sets, the team tested how much chemistry tracked plant lineage versus fungal presence. They found that host phylogeny—the evolutionary history of the grasses—and the fungal groups together accounted for 62.9% of the chemical differences. Importantly, fungal partnerships alone accounted for 27.4% of the chemical variation, totally free from plant relatedness. Different fungal OTUs lined up with distinct chemical reaction pathways, proving that fungi leave clear fingerprints in leaf tissues.

What we still do not know

These results give fresh clues about plant defense and how non-native grasses spread. Even so, the study had clear bounds. Because leaves and fungi were tested as one whole blend, scientists could not tell which partner produces each compound. Is the fungal guest making the compounds on its own, or does it trigger the plant to brew them? The exact steps linking these fungal groups to plant defenses remain an open puzzle.