The He Hang-Deng Xingwang team successfully constructed the T2T genome maps of two kiwifruit species

Under the condition that China's arable land area is limited, greatly improving crop yield and quality is an inevitable way
to meet agricultural security and develop agricultural economy.
With the application of agricultural big data and modern biotechnology, more and more species have entered the era of breeding 4.
0, that is, precision design breeding, one of the representative symbols is the analysis
of T2T (telomere to telomere) complete genome and T2T pangenome.
Following the first cracking of the T2T gap-free genome of watermelon in June 2022, on December 31, 2022, the team of He Hang and Deng Xingwang of the College of Modern Agriculture of Peking University and the team of Zhong Caihong of Wuhan Botanical Garden published an online report entitled " Two haplotype-resolved, gap-free genome assemblies of Actinidia latifolia and Actinidia chinensis shed light on regulation mechanisms of vitamin C and sucrose metabolism in kiwifruit The research paper reports on the T2T gapless genome map of broad-leaved kiwifruit and Chinese kiwifruit, and integrates genome, transcriptome and metabolome multi-omics analysis to deeply explore the kiwifruit fruit quality regulatory genes, which provides an important resource
for the research of kiwifruit functional genes and molecular breeding.

Unnotched genome map of Chinese kiwifruit and broad-leaved kiwifruit

Kiwi fruit is a fruit with extremely high edible value, and is known as the "king of fruits"
because it is rich in vitamin C, organic acids, minerals.
According to statistics, in 2019, China's kiwifruit harvesting area and output reached 182,600 hectares and 2,196,700 tons respectively, accounting for more than
half of the world's total output and planting area.
Actinidia originated in China, and the genus contains a total of 54 species, of which 52 are mainly distributed in China
.
Although the history of kiwifruit in China is more than a thousand years, breeding research and industrial development have long lagged behind New Zealand, Italy and other kiwifruit scientific research and production countries
.
At present, the basic research and molecular breeding of kiwifruit are mainly limited by the few available germplasm resources, and only the genomes of Chinese kiwifruit and hairy kiwifruit have been published, which seriously restricts the genomics research and genetic improvement
of kiwifruit.

The research team selected broadleaf kiwifruit with ultra-high vitamin C content and the excellent variety of Chinese kiwifruit "Donghong" with independent intellectual property rights in China as the research objects, and completed the splicing of two telomere-to-telomere gapless kiwifruit genomes by integrating deeply sequenced PacBio HiFi, Hi-C, ONT data, and obtained chromosome-level haplotype genomes
.
By constructing the phylogenetic tree with a conserved single copy of homologous genes, it is inferred that the divergence between broadleaf kiwifruit and Chinese kiwifruit is about 8.
39 million years ago
.
During this period, 189 gene families experienced significant gene multiplication, while 58 gene families experienced gene loss
.
The expansion and contraction of these gene families may be associated with
traits specific to the kiwi family, such as higher vitamin content and larger fruit size.
The study found that the distribution of vitamin synthesis pathway genes in different kiwifruit species was relatively conservative, but its expression pattern was not exactly the same
in materials with high vitamin C content (broadleaf) and low vitamin C content materials (eastern red).

Compared to broadleaf kiwifruit, eastern red kiwi fruit has significantly higher sweetness
.
Extensive targeted metabolome and transcriptome sequencing of fruits 30, 60, 95 and 135 days after flowering was used to enrich sugar alcohol metabolites
in metabolites in the late stage of fruit development.
After correlation with the transcriptome, a sucrose transporter gene, AcSWEET9b, was identified, with an expression pattern
significantly correlated with the content of sucrose.
The overexpression and gene silencing of the gene were carried out, and it was found that the sucrose content of the overexpressed material was significantly increased relative to the wild type, and the content of the opposite gene silencing material was significantly reduced
relative to the wild type sucrose.
By comparing and analyzing the AcSWEET9b gene sequence and fruit sucrose content in the Red Heart Chinese Kiwifruit taxa, wild Chinese Kiwifruit taxa, and wild Kiwifruit species taxa, it was found that the promoter regions of the gene were quite different, and the promoter haplotype was fixed in the sweeter Red Heart
Kiwifruit taxa.
Therefore, the AcSWEET9b promoter region was artificially selected during the domestication of AcSWEET9b Kiwifruit, which may be an important reason for
the increase in sweetness of AcSWEET9b Kiwifruit.

Han Xue, postdoctoral fellow at the College of Modern Agriculture, Peking University, Zhang Yilin, a doctoral student at the College of Modern Agriculture, Peking University, and Zhang Qiong, associate researcher at the Wuhan Botanical Garden of the Chinese Academy of Sciences, are the co-first authors of the paper.
Researcher He Hang, Researcher David Li and Academician Deng Xingwang are co-corresponding authors; Dr.
student Ma Ni of Peking University, Liu Xiaoying, assistant researcher of Wuhan Botanical Garden, Tao Wenjing, master student of Xiamen University, and Lou Zhiying, research assistant of the Institute of Modern Agriculture of Peking University, participated in the research, and Zhong Caihong, researcher of Wuhan Botanical Garden, made important contributions
to this research.
The research was supported
by the Natural Science Foundation of Shandong Province, the Science and Technology Innovation Project of Shandong Province, the Dean's Fund of the Institute of Modern Agriculture of Peking University, and the Postdoctoral Program of Liberal Arts of Peking University.

Original link: https://doi.
org/10.
1016/j.
molp.
2022.
12.
022