Grasses provide most of the world's calories—but we're only now starting to learn how they grow

The next time someone tells you that something is "as boring as watching the grass grow," you might want to remind them that corn, wheat and rice — three of the most important food crops on Earth — are all grasses. And those three crops alone provide most of the plant-based calories that feed the world's 8 billion people, plus the calories fed to livestock.

Now, thanks to new research from the University of Massachusetts Amherst, scientists have finally cracked a mystery about how these vital plants grow — and the answer challenges what researchers thought they knew about plant biology.

Samuel Hazen, a professor of biology at UMass Amherst, led a team that discovered grasses grow according to temperature, not light. This is surprising because most other plants on Earth respond to light cues to trigger their growth cycles.

"All the things we thought we knew about the timing of daily growth rhythms in plants turn out to be different in the plants that provide almost all of our calories and most of the calories that we feed to the animals we eat," Hazen said.

The team made this discovery by engineering a type of grass called purple false brome to glow whenever its stem cells grew. They linked a gene called CESA8 — which builds the stiff walls that hold up plant stems — to firefly luciferase, the enzyme that makes fireflies light up.

"For the first time, we are now able to watch a gene responsible for building the plant's structural support turn on and literally glow inside a living stem," said Greg Gregory, a graduate student at UMass Amherst who was the study's first author.

The researchers found that grasses grow fastest when there are warm temperature pulses during cool nights, and slowest when cool pulses interrupt warm days. In general, the plants grew faster during cool nights and slower during warm days.

Gregory and co-author Dave Follette designed a custom imaging system that could take time-lapse pictures of the glowing plants as they grew under different conditions.

The findings, published in the journal Current Biology, could help farmers and scientists breed more resilient crops as the climate changes. If we know grasses respond to temperature rather than light, we might be able to develop varieties that grow better in warmer or cooler conditions — which could mean more food for everyone.