The researchers are tracking the root of increased hybrid viability in maize through to differential translational fractionation of its subgenomes
The saying goes: "Two are better than one." Well, that may be true for endeavors involving human heads, but when it comes to ears, hybrid corn has a superior advantage over the parent herds in most cases. This phenomenon, known as hybrid vitality or “heterosis”, has been used by farmers for centuries to produce higher-yielding, more resilient varieties of corn around the world.
But what are the factors that contribute to the increased hybrid power of corn? Various genetic models have been proposed to explain heterosis in different cultures, including maize, but none have been able to fully solve the mystery of heterosis.
One possible reason for this could be the complex genetic origin of today's Zea mays maize. Corn is believed to have deviated from sorghum during an ancient speciation event, whereupon all of the chromosomal material or genomic set in the ancestral strain was duplicated through a process called polyploidization, creating an ancestral tetraploid, or a plant with the strain, i.e. four genomic sets twice as many as usual. Each genomic set in this tetraploid maize ancestor, referred to as the subgenome, went through dramatic breaks and amalgamations to eventually give rise to the current diploid genome (which carries two sets of genetic material). During this genomic reorganization, redundant copies of genes from both subgenomes were lost through a process called fractionation.
In plants in which such fractionation has been identified, including corn, there is a tendency for one subgenome to have more gene loss than the other – a process known as fractionation bias. For example, the two subgenomes in today's maize, referred to as maize1 and maize2, show a different expression of the constituent genes, with maize1 typically being identified as the dominant between the two.
It could be that the differential expression of proteins encoded by the maize subgenomes is responsible for the increased vitality of the hybrid maize lines designated as F.1. However, this has not been clearly established. Until now.
Now researchers in China have studied the transcriptome (the full complement of protein-encoding mRNA molecules obtained from information encoded in DNA) and the translatome (the actual set of mRNA that is translated into proteins in cells) of maize to identify possible factors responsible for heterosis in corn.
Using the new ribosome profiling technique, the researchers, led by Professor Lin Li of the National Key Laboratory of Crop Genetic Improvement at Huazhong Agricultural University, evaluated the maize parent lines B73 and Mo17, as well as their F.1 Offspring. Your results, published in The harvest journalindicate the presence of a pronounced subgenome distortion at the translation level, especially in the direction of translated subgenome maize1 genes, which had a non-additive effect on heterosis in F.1 Plants.
In addition, some genes in the hybrid surprisingly switched to the dominant form than in the parent lines. Prof. Li notes: “More genes have switched the dominant isoforms between the Fs1 and the two parents as between the two parents. This observation shows that the best gene variant in a given environment is more likely to be used selectively in hybrids, which leads to a higher efficiency of protein accumulation in the hybrids. "
In addition, the switched genisoforms mainly belonged to subgenom maize2, while the conserved genisoforms belonged to subgenom maize1. This knowledge, the researchers suggest, can aid selective breeding to further improve hybrid vigor.
In addition, the researchers found evidence of additive effects of gene expression on both the transcriptome and translatome level in the hybrid. According to Prof. Li, "All of these results agree with the Goldilocks hypothesis, suggesting that additive expression is beneficial for both the transcriptome and the translatome."
These results suggest the possible role of asymmetric subgenome translation as an important factor in corn heterosis. These findings can provide plant breeders with powerful genetic engineering tools to increase the yield of not only corn but also other food crops that could serve to address the threat of food shortages in the face of growing human populations around the world.
Authors: Wanchao Zhu (a), Sijia Chen (a), Tifu Zhang (b), Jia Qian (a), Zi Luo (a), Han Zhao (b), Yirong Zhang (c), Lin Li (a)
Title of the original paper: Dynamic patterns of the translatom in a hybrid triplet show translational fractionation of the maize subgenomes
Diary: The harvest journal
DOI: 10.1016 / j.cj.2021.02.002
(a) National Key Plant Genetic Enhancement Laboratory, Huazhong Agricultural University, Wuhan 430070, Hubei, China
(b) Jiangsu Provincial Key Laboratory for Agrobiology, Institute of Germplasm Resources and Biotechnology, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, Jiangsu, China
(c) Key Laboratory for Plant Heterosis and Use (MOE) and State Key Laboratory for Agrobiotechnology, Key Laboratory for Plant Genomics and Genetic Enhancement (MOA), Beijing Key Laboratory for Plant Genetic Enhancement, China Agricultural University, Beijing 100193, China
About Professor Lin Li
Professor Lin Li is the lead researcher at the National Key Laboratory of Crop Genetic Improvement at Huazhong Agricultural University (HZAU). He received his PhD in Plant Genetics from China Agricultural University in 2010 and joined HZAU in 2016 after completing his postdoctoral training at the University of Minnesota, Twin Cities. His current research area is corn plasma and systems biology.