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Scientists from Embrapa and the Federal University of São Carlos (UFSCar) are carrying out the genetic sequencing of the chestnut tree (Bertholletia excelsa), an icon tree of the Amazon rainforest not only for its size and exuberance, but for its social, economic importance and as a key species for forest conservation. The unprecedented study has already produced important genomic information and one of its greatest contributions will be in accelerating the genetic improvement of the species.
As it is a tree with a long life span, with classical genetic improvement, it would take around 50 to 200 years to evaluate the complete cycles and select the best plants to obtain the desired characteristics. This is because the researcher has to study the behavior of different plants in different environments and situations throughout their entire life cycle to obtain the desired answers.
However, through genomic sequences and bioinformatics, using gene banks available for other plants, it will be possible to find genes that indicate important characteristics, such as drought tolerance, resistance to pathogens or reproductive compatibility, for example. In this way, plants with the best profile are quickly selected, through genetic analysis.
Another important factor is that the chestnut tree is a species that presents genetic incompatibility, that is, there are individuals in the species that are unable to reproduce with each other and produce fruit. This makes identifying plants that are compatible or not essential. And the sequencing work already contributes to this challenge, the reference genome of the chestnut tree revealed the presence of reproductive incompatibility genes, bringing opportunities for the use of genomic tools in the improvement, planting and conservation of the species. The recognition of the determinants of genetic compatibility between individuals can facilitate the selection of matrices to be used in breeding programs and contribute to increasing the productivity of chestnut trees.
Using the DNA of a chestnut seedling, it will be possible to identify the genetic group to which the seedling belongs, thus guiding the choice of individuals to be used in commercial plantations.
“In addition, other genes of interest can be identified, favoring the selection of the best plants even in the nursery phase and gaining many years of research in the breeding program, offering safe and much faster results,” explains the Embrapa Rondônia researcher, Lucia Wadt.
Another interesting point is that natural selection for the adaptation of chestnut trees in each environment leaves marks on the plant's genome, just as the study of these marks is important both for the conservation of the species in forests and for the selection of trees in breeding programs. genetics to enhance fruit production. This research is conducted by Embrapa in partnership with UFSCar, through the EcogenCast project. The work began in 2016 and is ongoing.
In addition to identifying genes of agronomic interest, scientists also want to understand the influence of the environment in structuring genetic variability in native chestnut trees. This is expected to support conservation strategies, based on the evolutionary history of the species, its current and future geographic distribution. “The study also seeks to identify regions where chestnut tree populations may be more vulnerable to climate change, and by extension, reflect the vulnerability of several other species that occur in association with chestnut trees”, adds UFSCar researcher, Karina Martins.
According to the researchers, in an initial analysis carried out with 30 populations distributed throughout the Brazilian Amazon, it was possible to observe that the native chestnut plantations explored present genetic diversity, but with differences between regions. This means that the conservation of the species' diversity depends on the maintenance of chestnut trees in the different regions where it occurs. “Results from this type of research can be useful for defining priority areas for genetic conservation of the species, as well as recommending key populations for collecting genetic material to be used in the chestnut tree improvement program”, comments Wadt.
In addition to these aspects of conservation and improvement, the study will contribute to modeling the impacts of global climate change on forests, potentially helping to define actions to combat climate change and its impacts, contributing to 13 of the 17 Sustainable Development Goals (SDGs). ), which are part of the global agenda adopted by the United Nations for Sustainable Development.
To provide support for different genomic projects of the species, the reference genome of the chestnut tree was assembled, through a partnership between Embrapa, UFSCar and the University of Brasília (UnB), with funding from the São Paulo State Research Support Foundation. Paulo (Fapesp).
Researcher Karina Martins explains that the DNA of a native chestnut tree, located in Porto Velho, Rondônia, was sequenced and, with the use of computational tools, it was possible to assemble the entire genome of the species almost completely and with very high quality. The RNAs obtained from different chestnut tissues were sequenced and used to identify the genes in the assembled genome and search for their functions. “The public availability of the reference genome of the chestnut tree will be a fundamental resource for advancing knowledge about the species, contributing to the conservation of populations and their genetic improvement”, reinforces the researcher, adding that, for example, a large number of genes that confer resistance to pests and diseases and genes associated with selenium metabolism.
Interestingly, when comparing the genomic sequences obtained for chestnut with genomic databases, a strong association was identified with a bacterium that is pathogenic for sweet corn and other crops, causing Stewart's wilt. The work, which will be published soon, suggests that the association with the bacteria could be beneficial for the chestnut tree, since, in addition to the absence of virulence genes, multiple genes were identified in the microorganism potentially associated with growth traits in plants.
Many questions linked to the conservation of the species, sustainable use and cultivation of chestnut trees with a view to producing Amazon nuts and combating climate change can be answered with these studies. For researcher Lúcia Wadt, with the sequenced genome it will be possible to define genetic markers that can be compared with gene databases that already designate characteristics such as disease resistance and drought tolerance, for example. In this way, it will be possible to identify brands that shorten the path to selection of superior plants, thus facilitating the recommendation of genetic material for commercial plantations.
Chestnut metabolism associated with selenium is another item of research interest. Studies have already shown that trees that are in the same environment have different levels of selenium, which means that they have different metabolisms for absorbing and making this element available to the seeds. “Based on genetic markers, it may be possible to select plants with desirable characteristics in terms of selenium, for example. Furthermore, who knows, perhaps we have discovered how the genetic mechanism works that allows the plant to capture selenium from the environment and concentrate it in the seed. With this knowledge and advanced genomic techniques, it will be possible to enrich other foods such as peanuts, beans and other nuts, improving the nutritional value of foods. This is just an example of what can be done. Research into chestnut genomics opens up a world of possibilities”, concludes Lúcia Wadt. She predicts that, within two years, even more complete answers will be obtained from this genomic work.
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