Genetic breakthrough in cereal crops could help improve yields around the world

A team of scientists from Clemson University has achieved a breakthrough in the genetics of cereal crop senescence, with the potential to significantly influence the future of food security at the time of the world. climate change.

Collaborative research, which explores the genetic architecture of the poorly understood process of corn (corn) senescence and other cereal crops, has been published in The plant cell, one of the best scientific journals specializing in plant sciences. Rajan Sekhon, a plant breeder and assistant professor in the Department of Genetics and Biochemistry at the College of Science, is the principal author and corresponding author of the article entitled "The Analysis Integrated to the The genome scale identifies new genes and networks that underlie maize senescence.

"Senescence means" the death of a cell or organ in the hands of the very organisms of which it is a part, "Sekhon said." This happens everywhere, even in animals. We eliminate cells that we do not need. When the weather changes in autumn, we have these beautiful autumn colors in the trees. In early autumn, when the plants realize that they can not maintain the leaves, they kill their leaves. It is all about the energy saving ".

As a result, the leaves die after their color. The energy recovered in the leaves is stored in the trunk or the roots of the plant and is used to quickly reproduce the leaves the following spring. This makes perfect sense for trees. But the story is quite different for some other edible plants, especially cereal crops such as corn, rice and wheat.

"These crops are maintained with great care and bring an excess of nutrients in the form of fertilizer by farmers," Sekhon said. "Instead of dying prematurely, the leaves can continue to produce food through photosynthesis." Understanding the triggers of crop senescence such as corn means scientists can modify the plant to benefit a hungry world.

Sekhon, whose research interests include molecular genetics, genomics, epigenetics and plant breeding, established his laboratory in 2014 as an assistant professor. He has played a key role in developing a "gene atlas" widely used by the corn research community. He has published several articles in peer-reviewed journals evaluating the regulation of complex plant features.

"If we can slow down the senescence, it can allow the plant to stay green – or not to age – for a longer period," Sekhon said. "Plant breeders select plants with late senescence without fully understanding how senescence works at the molecular level."

These plants, called "stay-green", are aptly named. They stay green longer, produce better yields and are more resilient to the environmental factors that stress plants, including drought and heat.

But even with the existence of plants remaining green, there has been little understanding of the molecular, physiological, and biochemical foundations of senescence. Senescence is a complex trait affected by several internal and external factors and regulated by a number of genes working together. Therefore, the genetic approaches available on the market do not completely solve this enigmatic process. The breakthrough of Sekhon and his colleagues resulted from a systems genetics approach.

Sekhon and the other researchers studied the natural genetic variation of the trait remaining in corn. The process involved the cultivation of 400 different types of maize, each genetically distinct based on the DNA fingerprint (ie, the genotype), and then the extent of their senescence (c & # 39; that is, the phenotype). The team then linked the "genotype" of each line with its "phenotype" to identify 64 candidate genes that could orchestrate senescence.

"The other part of the experiment was to take a green plant and a plant that is not yet and to examine the expression of about 40,000 genes during senescence, "said Sekhon. "Our researchers examined samples every few days and asked what genes were gaining expression during this period, which allowed us to identify more than 600 genes that appear to determine whether a plant will remain green or not.

"One of the big problems with each of these approaches is the occurrence of false positives, which means that some of the genes detected are moats and examples of false negatives, which means that we lack some of the genes responsible . "

As a result, Sekhon and his colleagues had to carefully combine the results of the two large experiments using a "steam genetics" approach to identify certain high confidence target genes that can be further tested to confirm their role in senescence. They combined sets of data to narrow the field to 14 candidate genes and, ultimately, examined two genes in detail.

"One of the most remarkable discoveries has been that sugars seem to dictate senescence," Sekhon said. "When sugars are not far from the leaves where they are made via photosynthesis, these sugar molecules begin to send signals to initiate senescence."

However, not all forms of sugar present in plants can be reported. One of the genes discovered by Sekhon and colleagues in this study appears to break the complex sugars of leaf cells into smaller sugar molecules – six-carbon sugars like glucose and fructose – capable of relaying the senescence signals.

"It's a double whammy," Sekhon said. "We are not only losing these extra sugars made by plants that can feed more hungry mouths, these unused sugars in the leaves begin senescence and stop the process of synthesizing sugars all together."

The implications are enormous for food security. The sugars made by these plants should be diverted to various organs of the plant that can be used for food.

"We found that the plant was carefully monitoring seed filling, and this separation of sugar is a key factor in senescence, which we found is that there are many genetic variations, even in corn cultivars. grown in the United States. "

Some plants fill the seeds and can then begin to fill other parts of the plant.

"At least some of the remaining green plants can do this by storing extra energy in the stems," Sekhon said. "When the seed is harvested, all that remains in the field is called" catch-all ".

Stover can be used as animal feed or as a source of biofuels. With increasing demand for food and energy, there is growing interest in the development of dual-purpose crops that provide grain and fodder. As farmland becomes scarce, aging plants are becoming more important as they produce more energy per plant.

The genes identified in this study probably perform the same function in other cereal crops, such as rice, wheat and sorghum. Sekhon said the next step was to examine the function of these genes with the help of mutants and transgenics.

"The ultimate goal is to help the planet and feed the growing world.With the increasing deterioration of the climate, the contraction of land and water resources and the increase of the population, food security is the main challenge of humanity, "said Sekhon.