Cornell scientists develop cold-resistant corn

Professor David Stern examines test corn plants at Boyce Thompson Institute with Coralie Salesse-Smith. They are looking for varieties that will be better able to cope with cold weather. | Boyce Thompson Institute photo

Corn is the third largest grain crop in Canada and the number one crop in Ontario in terms of production. Nationally, yields vary depending on weather, and 2019 was a particularly challenging year.

Heavy rain and colder than normal temperatures made planting conditions difficult in Eastern Canada. Very dry conditions persisted into the growing season in parts of Western Canada, while unseasonal rain and early snow on the Prairies slowed harvest for many farmers.

Corn is one of the world’s most important crops, not only for food but for animal feed and biofuel. However, as a grass of tropical origin, it is particularly sensitive to cold weather. That trait can be problematic, especially when the growing season is only four or five months.

At Cornell University’s Boyce Thompson Institute in New York, scientists have developed a chill-tolerant corn variety that recovers much more quickly after a cold snap. It could broaden the latitudes in which corn can be grown and help farmers increase yields, especially in the face of wildly fluctuating weather patterns due to climate change.

“While the research is too early-stage to know for sure, the chilling-tolerant corn has promise to help crops cope with early cold snaps, as well as recover more quickly from drought,” said David Stern, president of the Boyce Thompson Institute and adjunct professor of plant biology in Cornell University’s College of Agriculture and Life Sciences.

“In terms of cold snaps, the combination of cold weather and strong spring sunlight can cause corn leaves to bleach, weakening or even killing the plants. The chilling-tolerant corn is less prone to bleaching, allowing it to recover more quickly. As a result, farmers could potentially plant earlier and harvest earlier, avoiding the frequent drought-prone conditions of late summer that occur just when ears are filling with grain. The potential benefits are a more flexible spring planting schedule, and an earlier harvest.”

Research in 2018 showed that increasing levels of an enzyme called rubisco led to bigger and faster-maturing plants. Rubisco is needed by plants to turn atmospheric carbon dioxide into sugar but, in cold weather, its levels in corn leaves decrease dramatically.

“Plants are very good at sensing temperature and seem to deliberately reduce the amount of rubisco when it’s cold,” said Stern.

“In doing so, plants can save the energy it takes to make rubisco and other proteins, as well as generally slow down metabolism, just like many living organisms do in the cold (think of hibernation).”

Rubisco is made up of proteins — eight large subunits and eight small ones with help from a third protein called RAF1. Because rubisco is a protein, it is made up of amino acids, which are rich in nitrogen, making rubisco a nitrogen reservoir. However, Rubisco is actually an inefficient enzyme so boosting its function will boost plant growth.

“We introduced transgenes that increase the abundance of (the) three proteins: the large subunit of rubisco, the small subunit and RAF1,” said Stern.

“In the modified corn, all three proteins are more abundant, thus increasing the level of Rubisco.”

The scientists grew plants for three weeks at 25 C, lowered the temperature to 14 C for two weeks and then returned it to 25 C, which is a considerable temperature swing. The intent was to test resistance and monitor the factors that can help plants withstand stress.

“The corn with more rubisco performed better than regular corn before, during and after chilling,” said Coralie Salesse-Smith, a PhD candidate in Stern’s lab during the study and the research paper’s first author.

“We were able to reduce the severity of chilling stress and allow for a more rapid recovery.”

Compared to traditional corn, the genetically modified corn had higher photosynthesis rates throughout the experiment and recovered more quickly from the chilling stress with less damage to the molecules responsible for photosynthesis. As a result, the plant grew taller and developed mature ears more quickly following a cold spell.

“What scientists are trying to build into plants is resilience — the ability to withstand a variety of shocks whose frequency and magnitude cannot be reliably predicted,” said Stern.

“In the laboratory, we can only test a small number of simulated climactic conditions. What happens when cold is combined with drought? Flooding with a heat wave? The real world of agriculture is far more complicated than a lab study. So, putting this kind of corn in the field is the best way to test its resilience.”

He said that the technology to bolster corn into a chill-resistant variety is being tested for the first time this growing season by a large seed company. They will know later this year or early next year if the plant is responding the way they expect and if it works as well in their elite field varieties as it does in the laboratory.

“If it does, the traits would move into their standard breeding pipeline and farmers would see the seed in six to 10 years. That is the reality of breeding for new corn traits,” said Stern.

Meanwhile, several research projects continue.

“One is to improve the activity, or speed, of the rubisco enzyme,” he said.

“In corn, only about 70 percent of the enzyme is working at any given time. We would like to increase that to 80 percent or 90 percent. Another path is to combine the rubisco trait with other genes that can increase photosynthesis. Rubisco is only one player in a complicated metabolic network, and we need to target other steps in the pathway as well. A third direction is to combine this higher photosynthesis-chilling tolerance trait with genes that improve tolerance to insects, drought or heat. This moves towards the ‘optimal’ resilient and climate-ready plant that would be a long-term goal.”

It is possible this approach could be used on other crops such as sugar cane and sorghum. The research paper was published online in the Plant Biotechnology Journal.

Humans couldn’t pronounce ‘f’ and ‘v’ sounds before farming developed

By Alison George

Human speech contains more than 2000 different sounds, from the ubiquitous “m” and “a” to the rare clicks of some southern African languages. But why are certain sounds more common than others? A ground-breaking, five-year investigation shows that diet-related changes in human bite led to new speech sounds that are now found in half the world’s languages.

More than 30 years ago, the linguist Charles Hockett noted that speech sounds called labiodentals, such as “f” and “v”, were more common in the languages of societies that ate softer foods. Now a team of researchers led by Damián Blasi at the University of Zurich, Switzerland, has pinpointed how and why this trend arose.

They found that the upper and lower incisors of ancient human adults were aligned, making it hard to produce labiodentals, which are formed by touching the lower lip to the upper teeth. Later, our jaws changed to an overbite structure, making it easier to produce such sounds.

The team showed that this change in bite correlated with the development of agriculture in the Neolithic period. Food became easier to chew at this point, which led to changes in human jaws and teeth: for instance, because it takes less pressure to chew softer, farmed foods, the jawbone doesn’t have to do as much work and so doesn’t grow to be so large.

Analyses of a language database also confirmed that there was a global change in the sound of world languages after the Neolithic era, with the use of “f” and “v” increasing dramatically in recent millennia. These sounds are still not found in the languages of many hunter-gatherer people today.

This research overturns the prevailing view that all human speech sounds were present when Homo sapiens evolved around 300,000 years ago. “The set of speech sounds we use has not necessarily remained stable since the emergence of our species, but rather the immense diversity of speech sounds that we find today is the product of a complex interplay of factors involving biological change and cultural evolution,” said team member Steven Moran, a linguist at the University of Zurich, at a briefing about this study.

This new approach to studying language evolution is a game changer, says Sean Roberts at the University of Bristol, UK. “For the first time, we can look at patterns in global data and spot new relationships between the way we speak and the way we live,” he says. “It’s an exciting time to be a linguist.”

Journal reference: Science, DOI: 10.1126/science.aav3218

Fijian ants grow their own plant cities and farm tropical fruits

By Alice Klein

Ants beat us to it. A Fijian ant first started planting fruit crops 3 million years ago, long before human agriculture evolved.

The ant – Philidris nagasau – grows and harvests Squamellaria fruit plants that grow on the branches of various trees.

First, the ants insert seeds of the fruit plant in the cracks in tree bark. Workers constantly patrol the planting sites and fertilise the seedlings, probably with their faeces.

As the plants grow, they form large, round hollow structures at their base called domatia that the ants live in instead of building nests. When the fruit appears, the ants eat the flesh and collect the seeds for future farming.

Guillaume Chomicki at the University of Munich, Germany, and his colleagues discovered that each ant colony farmed dozens of Squamellaria plants at the same time, with trails linking each thriving hub. The connected plant cities often spanned several adjacent trees.

The researchers found that Squamellaria plants are completely dependent on the ants to plant and fertilise their seeds. At the same time, Philidris nagasau ants cannot survive without the food and shelter provided by the plants. The Fijian phenomenon is the first documented example of ants farming plants in a mutually dependent relationship.

Trees in nearby Australia have been observed with similar-looking ant-filled plants growing along their branches, but no one has known why, says Simon Robson at James Cook University in Australia. The plants are from the same family as Squamellaria, suggesting they have the same symbiotic farming relationship with ants.

Chomicki’s team also conducted a genetic analysis to study the history of the Fijian ant-plant interactions. The results showed that the ants lost their ability to build nests around 3 million years ago, at the same time as the plants developed roots that could grow in bark. This signals the beginning of the mutual relationship, which emerged when Fiji and Australia were still connected.

Brainy ants
Only a handful of other species have been found to farm their food. For example, Yeti crabs cultivate bacteria on their claws and sloths grow algae gardens on their fur. Ants have been known to cultivate fungi, but this is the first time they have been found to plant crops in such a mutualistic manner.

The fact that ants have developed such sophisticated food production skills confirms the impressive teamwork of ants, says Kirsti Abbott at the University of New England, Australia.

“Ants are a lot smarter than we think they are – we call them superorganisms because they form networks that are much like our brains,” she says. “The information flow among ant colonies is just insane compared to human social systems, so this finding does not surprise me in the slightest.”

Journal reference: Nature Plants, DOI: 10.1038/nplants.2016.181