Lettuce (Lactuca sativa L.), belonging to the Asteraceae family and Lactuca genus, is widely utilized as a fresh-cut vegetable and one of the most popular salad ingredients. With its rich nutritional content, crisp texture, and beloved taste, lettuce holds a special place in the hearts of consumers. It is abundant in vitamins, minerals, polyphenols, and carotenoids, offering numerous health benefits. In 2021, the global production value of lettuce reached 16.6 billion US dollars, with China, the United States, and Western Europe being the primary producers. However, the long history of cultivated lettuce has resulted in limited genetic diversity, making it vulnerable to various abiotic and biotic stresses. Therefore, molecular breeding in lettuce focuses on increasing yield, improving quality, and enhancing disease and pest resistance. Such efforts heavily rely on extensive genetic and genomic resources, including molecular markers and reference genomes. In 2017, the Michelmore team at the University of California, Davis published the genome of the Salinas lettuce cultivar, and in 2022, an improved reference genome, v11, was released. In 2023, the Beijing Academy of Agriculture and Forestry Sciences assembled the genome of stem lettuce (L. sativa var. Augustana). Although these assemblies have significantly facilitated lettuce/genetics research, they remain highly fragmented and incomplete, containing hundreds of gaps. Moreover, crucial regions such as centromeres, ribosomal DNA, and telomere sequences have not been reported, posing a bottleneck for functional genomics research, gene cloning, and molecular design breeding in lettuce.

 

 

On June 26, 2024, in the internationally renowned plant science journal "Plant Communications," the research team led by Associate Professor Li Guo from Peking University Institute of Advanced Agricultural Sciences published a research paper titled "The complete telomere-to-telomere genome assembly of lettuce." This paper unveiled the first gap-free telomere-to-telomere (T2T) complete genome sequence of lettuce (2n=18), covering 2.59 Gb. The study disclosed the highly complex genomic structure and repetitive sequence features of lettuce, shedding light on the three-dimensional genome architecture and epigenetic traits for the first time. These insights provide a significant contribution to our understanding of the complexity of higher plant genomes. Additionally, the research systematically predicted the nucleotide-binding site leucine-rich repeat (NLR) gene family, which includes disease resistance genes in lettuce, and analyzed their expression patterns during Botrytis cinerea infection, offering new clues for investigating the mechanisms behind lettuce's disease resistance.

 

 

Figure Lettuce's complete genome reveals centromere structure, epigenetics, and the landscape of NLR disease resistance genes

 

Co-first authors of the paper include Ke Wang, a joint graduate student from Peking University Institute of Advanced Agricultural Sciences and Shandong Agricultural University (PKU-IAAS), Jingyun Jin, an assistant researcher at the PKU-IAAS, and Jingxuan Wang, a research assistant. Associate Professor Li Guo from the PKU-IAAS is the corresponding author. The study received technical support from PKU-IAAS's Single-molecule Sequencing Platform and High-performance Computing Center. Funding was provided by the Key Research and Development Program of Shandong Province, the Shandong Provincial Natural Science Foundation's Outstanding Youth Science Fund, and the Shandong Provincial Taishan Scholar Program, among other projects.

 

Article link：https://doi.org/10.1016/j.xplc.2024.101011