The genetic and evolutionary genomics of the dominant group of modern maize hybrids has been revealed

Heterogeneous dominant group division of maize germplasm resources. Courtesy of the Chinese Academy of Agricultural Sciences

Recently, the research of the exploration and innovative utilization team of maize excellent germplasm resources of the Institute of Crop Sciences of the Chinese Academy of Agricultural Sciences, together with South China Agricultural University and the Institute of Biotechnology of the Chinese Academy of Agricultural Sciences, revealed the genetic law of convergence and heterogeneous selection of the dominant groups of maize father and mother, and analyzed the differentiation characteristics of maize genome and its contribution to the advantages of hybrids. By summarizing the past, the team theorized the practical experience of maize breeding, and provided theoretical guidance for the creation of maize inbred lines and the utilization of hybrid advantages in the new era. The research is published online in Nature Plants.

According to Wang Tianyu, a researcher at the Institute of Sciences, maize hybrids (single hybrids) have a strong hybrid advantage over their parents. Maize monocross is composed of inbred lines from the dominant group of mother and parent heterosis, respectively, and the heterogeneous mode refers to the grouping method with strong heterosis advantage after hybridization of individuals in a specific parent group and parent group. Since its large-scale production in the 1960s, its utilization rate has reached nearly 100%.

The history of breeding at home and abroad for more than half a century shows that the improvement of maize yield level mainly depends on the continuous improvement of the dominant groups of parent and mother hybrids and the optimization of the heterogeneous mode. However, the genetic improvement of the dominant group of paternal and maternal hybrids in the modern breeding process and its genomics basis are not clear.

The study collected and sorted out 1604 representative maize inbred lines with different breeding periods and different heterozygous dominant groups at home and abroad, covering the parent and mother groups of breeding applications in the main maize producing areas of the world, and carried out multi-environment, multi-angle phenotypic precision identification and resequencing-based genotype accurate identification for 21 agronomic traits.

An analysis of more than 3.05 million phenotypic data points and 220 million genetic variant loci found that there was both convergence and divergent selection in agronomic trait improvements in paternal and maternal groups.

The convergence selectivity traits are mostly related to the breeding goal of tolerance and high yield, which is manifested in the direction of parent group improvement towards earlier flowering, shorter loose-to-spin interval, lower panicle position, fewer male panicle branches, higher yield, higher row number, higher seed yield, larger grain size, and heavier grain weight.

The heterogeneous selectivity traits may be related to the maturation period and grain dehydration rate of the mother and her hybrids, which are manifested by the decrease of panicle thickness, panicle row number, and axial weight traits in the mother group and increase in the parent group.

On this basis, the team excavated a number of important genes and alleles related to the convergence and isotropic selection of traits in the paternal and maternal heterogeneous groups, and found that the accumulation of favorable alleles in the paternal and maternal heterogeneous groups was highly correlated with the improvement of convergence and heterogeneous traits.

Further studies have found that the genetic differentiation of some genomic regions between father and mother heterogeneous groups in the modern breeding process continues to increase, and the continuous differentiation of these genomic segments or genes is an important genetic basis for determining the advantages of maize hybrids.

In addition, the study further validated the role of the convergent selection genes ZmEMF1L1 and ZmKW10 and a differentiation gene ZmKOB1 in regulating maize flowering period, grain size, and heterosis in two modern breeding processes.

This study provides a solid theoretical foundation and genetic resources for the genetic improvement of paternal and maternal hybrid groups of maize hybrids, the breeding of strong dominant hybrids and the development of whole genome selective breeding technology.

Li Chunhui, associate researcher of the Institute of Science and Technology, is the first author, Dr. Guan Honghui, Jingxin of Nuohe Zhiyuan, Dr. Li Yaoyao of South China Agricultural University, and Wang Baobao, researcher of the Institute of Biotechnology of the Chinese Academy of Agricultural Sciences, are the first authors; Wang Tianyu and Li Yu, researchers of the Institute of Sciences, Wang Haiyang, professor of South China Agricultural University, Jeffrey Ross-Ibarra, professor of the University of California, Davis, and Jiao Chengzhi of Nuohe Zhiyuan are co-corresponding authors. The research has been funded by the National Key Research and Development Program, the National Natural Science Foundation of China, and the Science and Technology Innovation Project of the Chinese Academy of Agricultural Sciences. (Source: China Science Daily, Li Chen, Wei Fei)

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