Ancient hornwort hints at new ways to grow crops

Sequencing the genome of the ancient hornwort plant reveals genes that could help crops grow more efficiently with less synthetic fertilizer, researchers say.

Some 500 million years ago, when our continents connected in a single land mass and most life existed underwater—hornworts (Anthoceros) existed as one of the first groups of plants to colonize land.

Sequencing hornwort provides insights into the genetics underlying the unique biology of the group, researchers report.

The researchers began the project in 2011. “It took us three years to figure out how hornworts can be grown and pushed through its sexual life cycle under laboratory conditions, and another three years to properly assemble and annotate its genome,” says Péter Szövényi, a researcher at the University of Zurich and last author of the paper, published in Nature Plants.

Hornwort belongs to the oldest still existing land plants. (Credit: Michael Lüth/U. Zurich)

One of the researchers’ goals was to find genes that play a role in hornworts’ method of concentrating carbon dioxide inside chloroplasts, which boosts the plants’ ability to make sugar resulting in increased yield.

Hornworts are unique among land plants in this capability, but some species of algae share the trait. The researchers compared the hornwort genomes with those of algae and found one gene, LCIB, that the two groups share but other land plants don’t.

“If this carbon-concentrating mechanism could be installed in crop plants, then they could grow larger with the same amount of fertilizer,” says first author Fay-Wei Li, plant biologist at the Boyce Thompson Institute and Cornell University.

Furthermore, hornworts live in symbiosis with fungi and cyanobacteria providing phosphorus and nitrogen to the plant. The researchers also identified 40 genes that may promote the hornworts’ source of nitrogen, which comes from an interdependent relationship with cyanobacteria—a unique feature in land plants.

“If this capability of hornworts can be transferred to crop plants, many tons of nitrogen fertilizer could be saved,” Szövényi says.

Such a reduction in fertilizer could benefit the environment, since excess agricultural nitrogen frequently enters waterways, where it can cause deadly algal blooms. Szövényi and Li are already working on a project to understand the genetic mechanism underlying the symbiotic plant-cyanobacteria interaction.

The research also sheds light on the evolution of early land plants. Without stomata, most plants cannot take up carbon dioxide and thrive in the terrestrial environment. Therefore, stomata represent a key innovation in colonization of the terrestrial environment.

Nevertheless, until now researchers didn’t know whether stomata have evolved once or potentially multiple times independently in land plants. Hornworts possess stomata during their spore-producing phase.

“We found that the basic genetic toolkit governing stomatal development in flowering plants is shared with hornworts,” Szövényi says. This finding is consistent with the hypothesis that stomata have evolved only once in the most recent common ancestor of land plants.

Hornworts, liverworts, and mosses were among the first plants to colonize land, but how the three groups related to each other had previously not been clear.

“Our research shows clearly that hornworts, liverworts, and mosses are all more closely related to each other than they are to vascular plants. We also show that liverworts and mosses are more closely related to each other than to hornworts,” says Fay-Wei Li.

Source: University of Zurich

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