On the evening of July 18, the College of life sciences of South China Agricultural University Professor Wang Haiyang’s team from the State Key Laboratory for the protection and utilization of subtropical agricultural biological resources and the Guangdong Provincial Laboratory of Lingnan Modern Agricultural Science and technology, in conjunction with the team for the exploration and innovative utilization of excellent maize germplasm resources of the Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, and the maize functional genome innovation team of the Institute of biotechnology, Chinese Academy of Agricultural Sciences, are published in nature plants (impact factor 17.352) A research paper entitled”genetic insights into historical improvement of heterotic groups during modern hybrid maize breeding” was published online. The article revealed the genetic law of convergence and differential selection of heterosis groups of parents and mothers in maize, analyzed the differentiation characteristics of maize genome and its contribution to heterosis, and theorized the practical experience of Maize breeding by summarizing the past, It provides theoretical guidance for the creation of maize inbred lines and the utilization of Heterosis in the new era. In response to this work, the news comments of experts from Munich University of technology in Germany were distributed at the same time, and they were highly praised.
Corn is the largest crop in the world and China, and plays an irreplaceable role in ensuring global and China’s food security. Maize hybrids (monohybrids) have strong heterosis compared with their parents. Single cross maize has been widely promoted in production since the 1960s, and its utilization rate has reached nearly 100%. Maize Single Cross is a cross combination of inbred lines from female parent heterosis group and male parent heterosis group respectively, and Heterosis mode refers to the combination mode in which individuals in a specific female parent group and male parent group have strong heterosis after hybridization. For a long time, foreign countries (mainly the United States) have formed three major heterosis groups:SS line, NSS line and iodent line. In addition to introducing foreign SS, NSS and iodent germplasm resources, China has also formed new heterosis groups such as SPT, PA and Pb, which are unique in China. In production, SS and PA lines are often used as female parents, while NSS, iodent, SPT and Pb lines are often used as male parents. The breeding history of more than half a century at home and abroad shows that the improvement of maize yield per unit area (more than 3 times) mainly depends on the continuous improvement of heterosis groups of parent and female parents and the optimization of heterosis mode. However, in the process of modern breeding, the genetic improvement law and genomic basis of parent parent heterosis group are not clear, which leads to low efficiency, blindness and poor predictability of parent parent inbred line breeding and cross combination, and restricts the cultivation of breakthrough new maize varieties.
In order to reveal the genetic law and genomic differentiation characteristics of breeding selection of parental and maternal heterosis groups in the process of modern maize breeding, 1604 representative maize inbred lines from different breeding periods and different heterosis groups at home and abroad were collected and sorted out in this study. For 21 agronomic traits, accurate phenotypic identification in multiple environments and angles and accurate genotype identification based on resequencing were carried out, Through the analysis of more than 3.05 million phenotypic data points and 220million genetic variation loci, it is found that this research material covers the male parent group and female parent group used in breeding in major maize production areas in the world, and they have experienced”harmony but difference” breeding improvement, that is, there are both convergent and divergent selections in the improvement of agronomic traits. Convergent selection traits (both parents’ groups improved towards the direction of earlier flowering, shorter interval between loose pollen and silking, lower ear position, fewer branches of tassel, higher yield, more grains per row, higher seed yield, larger grain size, and heavier grain weight) are mostly related to the breeding objectives of high yield and density tolerance, The traits of differential selection (ear diameter, row number per ear, axle weight traits decreased in the female parent group, but increased in the male parent group) may be related to the maturity and grain dehydration rate of the female parent and its hybrids.
On this basis, the whole genome scanning and association analysis strategies were adopted to mine a number of important genes and alleles that were convergent and divergent with the traits of the parent and maternal heterozygous groups, and it was found that the number of favorable alleles accumulated in the parent and maternal heterozygous groups was highly correlated with the improvement of convergence and divergence. Further research found that in the process of modern breeding, the genetic differentiation of some genomic regions between parent and maternal heterozygous groups is increasing, and the continuous differentiation of these genomic segments or genes is an important genetic basis for determining maize heterosis. In addition, gene editing technology and transgenic technology were used to verify the role of two convergent selection genes zmemf1l1 and zmkw10 and a differentiation gene zmkob1 in regulating Maize Flowering, grain size and heterosis. This study provides a solid theoretical basis and genetic resources for the genetic improvement of male and female heterosis groups of maize hybrids, the breeding of strong heterosis hybrids and the development of whole genome selective breeding technology.
Li Chunhui, associate researcher of Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, is the first author, and Dr. Guan Honghui, Nuohe Zhiyuan, Jing Xin, Dr. Li Yaoyao, South China Agricultural University, and researcher Wang Baobao, Institute of biotechnology, Chinese Academy of agricultural sciences are the first authors; Professor Wang Haiyang of South China Agricultural University, researcher Wang Tianyu and researcher Li Yu of Institute of crop science of Chinese Academy of Agricultural Sciences, Professor Jeffrey Ross Ibarra of University of California Davis, and Jiao Chengzhi of Nuohe Zhiyuan are co correspondents. The research was supported by national key research and development plan, National Natural Science Foundation of China, science and technology innovation project of Chinese Academy of Agricultural Sciences and other projects.