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As an important part of agricultural germplasm resources, aquaculture germplasm resources are the necessary material basis for the original innovation of aquaculture and the promotion of the high-quality development of modern aquatic seed industry and aquaculture industry. China is the world's aquaculture power, currently facing the improvement of quality and efficiency, change the production mode and other major industrial problems, germplasm improvement is to achieve the transformation of new and old kinetic energy in the aquaculture industry, to promote the key elements of the healthy and sustainable development of the industry, and high-yield and high-quality varieties have been urgently needed by the aquaculture industry, only by independently mastering important core germplasm resources, creating excellent fist-type new varieties, in order to have the initiative in the competition of the seed industry. Carrying out research on the genetic basis and regulation mechanism of aquaculture biological growth and quality traits can provide theoretical and technical support for the cultivation of high-quality and high-yielding good breeds, and enhance the innovation ability of aquatic germplasm in China.
The National Key R&D Program "Blue Granary Science and Technology Innovation" key special project "Research on the Genetic Basis and Regulatory Mechanism of Aquaculture Biological Growth and Quality Traits" (hereinafter referred to as the "Project") focuses on the genetic analysis of aquaculture biological growth and quality traits, and provides theoretical basis and technical support for the cultivation of high-quality and high-yield aquatic varieties.
Deciphering, the mystery of the water generator genome
Genes store all the genetic information about the process of birth, growth, and demise of life. The project focuses on the economic traits of aquaculture organisms such as fish, shrimp and crabs, shellfish, algae, echinoderms, etc., and determines the research objectives: first, to construct a fine map of aquaculture biological genomes; second, to establish a technical system for the verification of the function of aquatic economic traits, breaking through gene editing technology; third, to explore key genes and regulatory elements for growth and quality traits, reveal the gene regulation network of traits, and analyze the genetic basis and regulatory mechanism of water generator growth and quality trait formation.
Constructing a fine map of the genome is to map the order of deoxyribonucleotides on all chromosomes of a certain organism. "Complete and accurate genomic information is an important basis for fine analysis of traits and molecular breeding." Hu Xiaoli, project leader and professor of Ocean University of China, introduced, "The project team has completed the construction of chromosomal-level genomic fine maps of 11 aquaculture organisms, which has laid an omics foundation for the fine localization of aquatic economic traits, the analysis of heterosis, genome-wide selection and molecular design and breeding. ”
According to Hu Xiaoli, the team of researchers Li Jiongtang of the Chinese Academy of Fisheries sciences constructed a fine genome map of tetraploid mirror carp and its ancestor species tiger skin fish and a relative species like bream catfish, and found that the two subgenomes of the carp increased the exchange of genetic information through homologous exchange and trans shear, and the homologous gene expression had a dose compensation effect and the main effect gene phenomenon, which provided important information for revealing the genetic regulation mechanism of polyploid biological traits such as carp. Associate Professor Wang Dongmei of Ocean University of China broke through the difficulty of higher genome assembly of nori as an algal symbiont, GC content and repeat sequence ratio in the genome, revealed that the expansion and co-expression regulation of antioxidant gene families are an important genetic basis for the generational adaptation of nori leafy bodies to extreme environments, and elucidated the genetic basis for the in-depth understanding of the growth and development of seaweed by carbonic anhydrase regulation of seaweed leaf bodies using air carbon dioxide when dry dew is dehydrated, and the filamentous sporophytes inhabiting shells using shell calcium carbonate as a carbon source, It is of great significance to guide the cultivation of seaweed seeds. In addition, through comparative genomics research, Xiaojun Zhang, a researcher at the Institute of Oceanology of the Chinese Academy of Sciences, revealed the expansion mechanism of simple repetitive sequences (SSRs) in the genome of Chinese shrimp and its impact on genome plasticity, suggesting the key role of SSR in the evolution of shrimp adaptability.
Regulation, fish intermuscular spine gene knockout
Molecularly designed breeding can enable the transition from "empirical breeding" to targeted and efficient "precision breeding", which can greatly improve breeding efficiency. Through the establishment of aqueous gene function verification and gene editing technology, the project verifies the key gene functions of growth and quality and analyzes the trait regulation network, reveals the genetic basis and regulation mechanism of growth and quality traits, studies the genetic regulation mechanism of new germplasm with economic value in terms of growth quality, explores key genes and regulatory elements with breeding value, and uses it for breeding to improve the ability and level of aquatic germplasm innovation. The project has made a major breakthrough in the cultivation of carp without muscle.
(Left) Micro-CT photo of crucian interminal spur mutant, (right) crucian carp wild type Micro-CT photo (Photo courtesy of Kuang Youyi, Heilongjiang Fisheries Research Institute, Chinese Academy of Fishery Sciences)
Fish intermuscular spines, commonly known as fish spines, from low to high bone fish, intermuscular spines have undergone an evolutionary phenomenon from simple to complex, and then degenerated. China's main breeding of bulk freshwater fish, such as blue carp, grass carp, silver carp, bighead carp, carp, crucian carp, tuantou bream and other carp fish generally have complex intermuscular spines, in addition to China, Brazil and other South American countries mainly farmed lipoperic carp also commonly have intermuscular spines. The presence of intermuscular spines in fish greatly limits their processing and export earnings, and also brings trouble and a certain risk of injury to people (especially children) when eating these fish. However, due to the delicious taste of these large freshwater fish with fish spines, the easy mastery of breeding technology and the historical culture and traditional consumption habits, the bulk freshwater fish with fish intermuscular spines occupy an important position in China's aquaculture industry, and the annual output of carp is about 20 million tons, accounting for 77.5% of all freshwater fish aquaculture production and 42.6% of all aquaculture animal production.
"Intermuscular spines are a key issue that has long affected the growth of processing and consumption of carps." Hu Xiaoli introduced, "Kuang Youyi, a researcher at the Heilongjiang Fisheries Research Institute of the Chinese Academy of Fishery Sciences, identified the key genes for the development of muscle spines in freshwater fish, and used gene editing technology to knock them out in carp and crucian carp, and obtained individuals without muscle spines at all. Combining this regulatory approach with breeding programmes is expected to lead to new pathways for the cultivation of boneless fish without muscle, thus facilitating the process of precise improvement of biological traits in aquaculture. ”
In addition to identifying key genes for the development of carp and crucian carp interminar spines and successfully achieving knockout, the project team established high-throughput mutant screening technology and rapid homozygous line construction technology, obtaining more than 500 carp and crucian carp mutants with intermuscular spine gene editing, including 30 mutants without intermuscular crucian carp. Professor Gao Zexia's team at Huazhong Agricultural University also clarified the ossification characteristics of interosseous bone in Tuantou bream, identified the key gene scxa that regulates the number of interoskeletal muscles of Tuantou bream, and constructed a sa mutant with a 70% reduction in intermuscular spines.
Regarding the growth and development of individuals with missing muscle spines/less muscle stings, Hu Xiaoli introduced: "After the relevant team tests, the bone development and reproduction of carp mutants without muscles are no different from the wild type. This shows that the lack of intermuscular spines does not affect the growth and development of fish, or it has little impact on the growth and development of farmed fish. In addition, it was not found that the nutritional value and meat quality of the missing intermuscular stingray were not significantly different from those of ordinary farmed fish. ”
In vivo determination of scallop closed shell muscle trait based on X-ray imaging (top) and detection equipment (bottom) (Photo: Hu Xiaoli)
Improvement of growth quality, research and development of shellfish trait detection technology and analysis of genetic mechanism
Shellfish are mostly edible, delicious and nutritious, in addition to fresh food, dried, pickled, canned products also have a great market. Many shellfish are also excellent Chinese medicinal herbs, such as pearls and nacre powder, abalone shell stone cassia and so on. Shells can be used to burn lime, make paint blenders, shell carvings and other crafts, and pearls are valuable ornaments. Shellfish farming has become an important industry to increase employment, promote rural economic development and improve the food structure.
Comparison of Haida golden shell (left) and ordinary scallop (right) (Photo courtesy of Hu Xiaoli)
More than 95% of China's shellfish are obtained from aquaculture, and about 5% are mainly obtained through fishing. Among them, more than 97% of China's shellfish product production comes from seawater. According to the Data Of Statistics, the output of marine aquaculture shellfish in 2019 was 14.8017 million tons, accounting for 71.67% of China's marine aquaculture production (20.6533 million tons). Farmed shellfish has become an important source of high-quality protein in China, and high-quality and high-yield varieties are urgently needed for high-quality industrial development. The project developed a precise determination technology for shellfish important traits, analyzed the formation and regulation mechanism of shellfish traits, and laid the foundation for efficient cultivation of shellfish seeds.
Scallops are farmed shellfish in bulk, and the closed shell muscle is its main edible tissue. "In the past, if you wanted to determine the size of the closed shell muscle or 'meat column' of scallops, you needed to kill the shells to open the shells, but even if you found individuals with excellent traits, you could not carry out large-scale breeding and breeding." Hu Xiaoli introduced, "If we want to solve this problem, we must realize the living and non-destructive determination of scallop closed shell muscle traits. ”
To this end, Professor Hu Xiaoli established a shellfish muscle in vivo and nondestructive determination technology based on X-ray imaging, broke through the technical bottleneck of scallop closed shell muscle difficult to be measured in vivo, and developed high-throughput measurement equipment, which has been applied to the cultivation of high closed shell muscle weight scallop seeds.
Carotenoids are a general term for natural pigments that appear yellow, orange-red, or red, and are commonly found in animals, plants, and microorganisms, in which animals cannot synthesize carotenoids, but can only obtain them from food. The Ezo scallop "Sea Golden Shell" is different from the ordinary Ezo scallop, due to the abundance of carotenoids, its closed shell muscle is orange-red, which is also the origin of the name of this species "Sea Golden Shell".
Why is the closed shell muscle of the "sea golden shell" enriched with carotenoids? Professor Hu Xiaoli conducted research on this and revealed the mechanism of carotenoid accumulation in the muscles of the Ezo scallop "Haida Golden Shell".
"We found through our research that the accumulation of carotenoids in the muscle of 'Haida Jinbei' is a recessive trait and is regulated by a gene of carotenoid cleavage oxidase PyBCO-like1." Hu Xiaoli told reporters, "The promoter mutation has led to a downward adjustment of the expression of the PyBCO-like1 gene, which reduces the metabolic breakdown of carotenoids, which is the reason why the 'Haida Golden Shell' is enriched with carotenoids and the closed shell muscle is orange-red." ”
"We have applied the PyBCO-like1 gene to the cultivation of carotenoid-rich scallops." Hu Xiaoli told reporters, "After we found that the PyBCO-like1 gene regulates the accumulation of carotenoids in scallop muscle, Canadian scholars reported that the relevant mechanism is also the cause of salmon muscle accumulation of carotenoids. This mechanism may have an impact on the regulation of carotenoid accumulation in other aquaculture animals. ”
The Hox gene, whose full name is homologous, is an important gene that regulates the development of animal body patterns. Researcher Gao of the Institute of Oceanology, Chinese Academy of Sciences, revealed the regulatory effect of Hox on the formation of shellfish tissue and organs, and proposed that the Hox gene has formed a new theory of the diversification system of living shellfish by regulating the development of back and abdominal organs, which provides a new understanding of the growth and development mechanism of shellfish, and also lays a foundation for the subsequent in-depth analysis of the regulatory mechanism of shellfish growth and development.
Author: Yang Yang
Source: China Rural Science and Technology, No. 8, 2021
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