Scientists at UC Davis have developed a new genetic tool that makes it easier to breed wheat and triticale to grow more efficiently and to be better adapted to different environments. This new tool is pushing a second Green Revolution, as it bypasses some of the complications left from the first one.

The new method recognizes that, in grasses such as wheat, small and short are different.

Developed by researchers in the Department of Plant Sciences, the method allows breeders to tease apart the genes that control plant height from genes that control other aspects of a plant’s growth and other qualities. With that, breeders can now develop varieties of grain with a range of plant heights, so farmers can get seed better suited to the conditions of individual fields.

“These are exciting times, as we now have advanced tools that allow us to leverage our knowledge of biology in support of breeders’ work,” said Juan Debernardi , manager of the Parsons Foundation Plant Transformation Facility at UC Davis and lead investigator on the project.

The team includes the lab of wheat geneticist Jorge Dubcovsky, a distinguished professor. Their breakthrough is so significant that Plant Biotechnology Journal put the team’s paper on the cover of the February issue. First authors on the paper are Chaozhong Zhang, a research associate on the team, and Joshua Hegarty, a project scientist with the UC Davis Small Grains Breeding Program.

New tool uses micro-RNA

Grasses, including wheat, naturally want to grow tall so the seeds that ripen at the top of their stems can spread far and wide. In the 1960s, Green Revolution scientists changed agriculture by breeding wheat and other food-producing grasses that would grow smaller and with more seeds, providing more food for the world. When the seeds of those grasses germinate, the sprouts are smaller, too -- so the seeds have to be planted closer to the surface for the tender sprouts to reach it.

In contrast, plants developed with the new method still grow short above the ground. What’s different is that germinating plants have normal-sized structures as they emerge from their seeds below ground. This means seeds can be sown deeper in the soil, letting the plants reach moisture stored there – a boon for farmers on water-challenged lands.

In addition, the shorter triticale the team developed with this method was less likely to fall over while growing. That problem is called lodging, which can make grain difficult to harvest mechanically and dramatically reduce grain yield. Lodging is what prompted Hegarty -- who heads the field testing -- to talk to Debernardi about genetic solutions.

“It took just two years — from our initial discussions with Josh about the lodging in his triticale lines to having the new varieties in the field” Debernardi said.

The team took a new approach, focusing on the genes AP2L-B2 and AP2L-R2 which, when activated, make plants grow shorter.

They employed a revolutionary new discovery: micro-RNA. These tiny molecules regulate gene expression in plants and animals, and just in 2024, their discoverers won a Nobel Prize in Physiology or Medicine. Micro-RNAs do many different jobs. Some kinds are like tiny scissors, Debernardi explained, cutting out bits of genes and reducing those genes’ impact.

Using the genetic editing tool CRISPR-Cas9, the team introduced mutations that block the ability of a particular micro-RNA whose job is to snip the AP2L2 genes. That means the levels of the AP2L2 genes in the new plants were higher, and those plants grew shorter above ground.

Furthermore, by snipping for different levels of AP2L2, the team could develop plants that grow at different heights.

Less breeding time, better grain yield

It’s a breakthrough for wheat and triticale breeders.

“The flexibility to create plants with different heights in a single step and without altering all the other characteristics of a variety, such as grain quality and disease resistance, is very appealing,” Debernardi said. “This process avoids the need of crossing the varieties with specific dwarfing genes and the required backcrossing process. All that usually takes many years.”

The method produced superior results outside the lab, too. In field tests over two years, gene-edited plants were 5 to 7 inches (12 to 18 cm) shorter and resisted falling over better during storms. This led to a significant reduction in lodging and a 9-percent total increase in grain yield, the team reported.