Grain – Ready for Climate Change?
With a genetic trick, biologists from Freie Universität Berlin are making barley plants more drought-tolerant.
Jun 17, 2019
Parched fields, shriveled cobs of corn, and grain that withers on the stalk. The summer of 2018 really packed a punch in Europe: High temperatures and low rainfall for long periods caused dramatic crop losses in many places. The affected farmers aren’t alone in wondering what will happen when extreme summers become more common in the course of climate change. You can’t wave a magic wand to get enough rainfall – but maybe plants could adapt to drier soil?
Thomas Schmülling has been working on that very question for some time now. Schmülling, a biologist and the head of the “Molecular Developmental Biology of Plants” group at Freie Universität Berlin, and his longstanding collaborator Eswarayya Ramireddy recently succeeded in making barley less susceptible to drought stress. “We reduced the hormone cytokinin, which normally suppresses root growth, exclusively in the roots of the barley plant,” Schmülling explains. That prompts the root network to grow better because there is less of the hormone available. To achieve this, the team of researchers boosted the activity of the gene that causes the formation of an enzyme called cytokinin oxidase. This is exactly the enzyme that breaks down the growth-impeding phytohormone in the roots.
Modified Barley Contains Significantly More Zinc
In a greenhouse, the researchers then sowed seeds of the genetically modified barley and conventional barley and measured the length and degree of branching of the roots in each group after two to four weeks. The result? The transgenic plants had formed significantly more roots, and their roots branched out more. “The really special thing was that we couldn’t find any negative effect on shoot growth,” Schmülling explains. That means the increased root growth does not come at the expense of the part of the plant above the ground.
So does that mean in a drought, the plant does not “notice” the stress until later because the larger root system means it gets an adequate supply even when there is little water retained in the soil? “Exactly. And since the normal response to lack of water is to stop growing, it might be the case that the shoot keeps growing even under stress and tolerates more extreme conditions.”
Drought stress occurs in many different scenarios, Schmülling explains. Depending on weather conditions, plants can encounter stress very early on, or not until late phases of growth. The lack of water might be deep in the soil or at the surface. “As a result, our observations from the greenhouse don’t translate to every possible scenario. But the results do give us hope.” And for a whole other reason, too: When the researchers examined the seeds of the new barley, they made a surprising discovery. They contained 40 to 50 percent more zinc than conventional grain.
“Zinc deficiency is one of the biggest nutrition problems worldwide, ranking with iodine and iron deficiency,” explains Schmülling. “About two billion people suffer from zinc deficiency, chiefly in developing countries.” This condition results in a weakened immune system, which in turn brings problems with growth and wound healing, along with lower fertility. Severe zinc deficiency contributes to mortality in young children.
With this in mind, one of the aims of the international initiative called HarvestPlus, which is supported by several aid organizations, is to increase zinc content in crops through targeted breeding. “The values for our plants are already above the targets set by the initiative, so this could help contribute to a lasting solution for dietary zinc deficiency,” Schmülling says, looking to the future.
Barley as a Model Plant for Wheat
The scientists have not yet studied in detail why the transgenic barley stores higher levels of zinc. “We think the plant might be able to tap into a larger soil volume due to the enhanced root growth. Cytokinin also regulates the formation of transfer cells in the roots. These are permeable cells in the root that are needed in order to absorb trace elements from the soil. Less cytokinin means more transfer cells can form.”
Barley also serves as a model plant for wheat, the most important food crop worldwide. But for genetic reasons, it is not a good fit for experimentation. Schmülling’s team had started their research with a different model plant, Arabidopsis (rockcress). The cytokinin experiments were highly successful in this plant, as were later trials involving tobacco and rape plants. Together with colleagues in the Belgian city of Ghent, the biologists in Berlin are currently working on corn. Initial results are expected in a few months.
Transgenic plants, or “green” genetic engineering, are a controversial issue. In these kinds of plants, methods drawn from molecular biology are used, like in Schmülling’s research group, to modify specific genes on a targeted basis. In traditional breeding, mutations are caused by chemical or physical influences, such as substances or radiation that change the plant’s genetic makeup. “When this method is used, a large number of genes undergo uncontrolled manipulation. After that, the mutated plants are crossed to create new combinations, and the most promising ones are selected,” Schmülling explains.
Breeding or genetic engineering – in Schmülling’s view, there are justifications for both. “Targeted plant breeding using modern methods from molecular biology may even be relevant in terms of organic farming in the future, since just like in conventional agriculture, it can be used to produce suitable varieties.”
Plants have various tricks they use to protect themselves against drought stress, up to a certain point. For example, they can close the pores, known as stomata, on their leaves or form a thicker waxy coating to reduce water loss. But in many species, that won’t be enough to make them adequately resilient in the face of climate change, Schmülling fears: “We don’t think enhanced root growth is the one solution to the problem – but it is one option, and one that is worth pursuing.”