Different forms of corn and grass.
Maize and seven subspecies of the ancestral wild syrup form a genus of maize in the family Poaceae. Despite being closely related, the plants in the genus Maize grow very differently and grow in a variety of environments. These properties make it an ideal model species for studying adaptive evolution.
Recently, the Yan Jianbing team of the National Key Laboratory of Crop Genetic Improvement and the Hongshan Laboratory of Hubei Agricultural University and the Jeffrey Ross-Ibarra team of the University of California, Davis and others published a paper online in Nature Genetics to construct a genetic variation map of maize and reveal the regulatory mechanism of its adaptive evolution.
Klaus F.X. Mayer, professor at the Helmholtz Center in Munich, Germany, said: "It is of great significance to study the genetic diversity of the herb in different regions, the evolutionary history of maize, etc., and studying the alleles lost in the process of domestication will open up new paths for genetic breeding." ”
Corn and its seven parents
Maize originated in southwestern Mexico, and its wild congenus is collectively known as the big grass, with 7 subspecies. Yan Jianbing, co-corresponding author of the paper, told China Science News that corn is not only the most widely planted crop in the world, but also one of the model species for basic research.
Although it is only found in Mexico and Central America, its subspecies can adapt to a variety of environments: some adapt to hot, humid Central American environments; Some adapt to the cold, arid environment of Mexico's central highlands.
"They are both maize genus, closely related and have a relatively short evolutionary history, about tens of thousands to hundreds of thousands of years ago." Yan Jianbing said that these characteristics of maize make it an ideal model species for studying adaptive evolution, which is conducive to capturing their genomic changes through the convergent selection angle of closely related species or origin species.
In August this year, Yan Jianbing's research group completed the super pan-genome map of the genus Maize. His team has built a consortium of diversity associations for maize and its wild material over the past 10 years, and has used this group to produce a range of research results.
"This study wanted to explore the commonalities of the various subspecies within the genus on the basis of the pan-genome of maize and its large number of genetic variations, that is, to find out what similarities exist between wild species under the conditions of natural selection and artificial selection of cultivated species." Yan Jianbing said.
Wild resource collection was the hardest part of the study. Chen Lu, co-first author of the paper, said that because it does not originate in China, wild samples are very difficult to obtain, and are only treasured in a few laboratories and gene banks around the world. In the global coronavirus pandemic, it is almost impossible to collect these samples with just one team. Fortunately, their foreign partners did their best to find enough samples.
"This is the hardest part of this experimental study." Yan Jianbing said. Finally, their conclusions came from the analysis of a total of 237 materials and 507 modern maize inbred materials from 7 wild subspecies of the genus Maize.
Nature vs Artificial: The Story of Convergent Evolution
The study found that different subspecies of the genus Maize began to differentiate about 120,000 years ago, and rapidly differentiated into the current seven subspecies about 68,000 years ago, one of which was further domesticated by humans into modern maize.
Chen Lu introduced that there is a large number of gene infiltration between different species of maize. Gene infiltration in genetics (especially plant genetics) refers to the flow of genes between two gene pools (e.g., two species or subspecies), usually through interspecific hybridization.
Gene infiltration is a long-term process. Yan Jianbing explained that any species has a direct ancestor, and if the genes of wild relatives directly enter the modern species and contribute to the genome of the modern species, it belongs to gene infiltration.
"The large amount of gene infiltration suggests that gene exchange may play an important role in crop adaptation." Yan Jianbing said that there is not enough evidence to understand the function of these unique genetic variants, which is also one of their future research directions.
Adaptive studies of different subspecies of maize have found convergent evolution at the genomic level.
"The phenomenon of convergent evolution is widespread in nature, and traits in which convergent evolution occurs often have important adaptive or economic value." For example, Yan Jianbing said that in the process of adaptive evolution, the genomic loci and differentially expressed genes of convergent selection of plateau grass and high-latitude (temperate) maize were significantly enriched.
Chen Lu further explained that both plateau grass and temperate maize have selected genes that control flowering during adaptation. Only those that have experienced natural selection must survive on plateaus with less accumulated temperature, and only early flowering can complete the transition from vegetative growth to reproductive growth before the temperature drops, and then bear fruit and live to the next year. This process is completely adaptation to the environment.
Maize was domesticated from the tropics and continued to spread to temperate regions, becoming one of the most widely cultivated crops today. In the process of adapting from low latitude to high latitude, corn must also adapt to changes in light temperature. It must also complete the reproductive process before the temperature drops, otherwise it will not be able to adapt to the high latitude environment.
"This result provides a reference for understanding the role of natural and artificial selection in the adaptive evolution of species." Yan Jianbing said.
The research team further screened a number of key genes that regulate the flowering period of maize, and used molecular biology to prove that a gene ZmPRR7, which is selected in both plateau grass and temperate maize, and ZmCOL9, which is selected only in temperate maize, play an important role in regulating the flowering process of maize.
Finding new genetic pools to combat climate change
"Climate change affects crop production, which further exacerbates the imbalance between inadequate food availability and population growth." Yan Jianbing said that human survival urgently needs new crop varieties, both to increase yields and to improve adaptability to different environments.
Although widely cultivated worldwide, maize still loses its rich genetic diversity during domestication and reproduction due to genetic bottlenecks (certain events can greatly reduce population size) and artificial selection. The ancestor of maize, wild sorrel, adapted to different environments, from hot, humid, subtropical regions to cold, dry, high-altitude regions. They exhibit biotic and abiotic adaptations (such as extreme environments and disease resistance) not found in modern maize, and provide rich genetic diversity that can be used for future breeding. However, little is known about the potential of large grass as a useful source of diversity for maize.
"In order to cope with future climate change, we must return to nature, find genetic resources from the wild resources of the big grass, expand the existing gene pool of corn, and meet the cultivation of new corn varieties that adapt to climate change in the future." Yan Jianbing said, "Addressing climate change is the biggest challenge we face, and it is impossible to complete the task if we only focus on the existing corn genetic resources." ”
Wei Li, editor of Nature Genetics, believes that this study carefully designed the sampling of germplasm resources of Agaricus da and constructed a high-density genetic variation map of Maize species, which not only provided the genetic diversity resources of the entire genus, but also expanded people's understanding of the potential application of convergent adaptation and adaptive evolution sites of Maize in maize improvement.
Yan believes that the population genetics of maize provides a large number of missing adaptive alleles in maize that have the potential to accelerate future breeding through the reintroduction of genetic diversity. (Reporter Li Chen)
Related paper information: https://doi.org/10.1038/s41588-022-01184-y
Source: China Science News