A study uncovers the genetic basis of leaf heading in lettuce. Lettuce (Lactuca sativa) comes in different varieties based on leaf architecture and arrangement. Unlike romaine, butterhead, and loose-leaf lettuce, crisphead, or iceberg, lettuce exhibits heading-a phenotype in which flat and expanded rosette leaves fold inward upon emerging to form a compact, spherical head. Heading facilitates harvest, improves leaf texture, and prolongs shelf life, but its genetic underpinnings are unclear. Hanhui Kuang and colleagues cloned a region of the lettuce genome that controls heading, which is considered an anomaly arising from discordant cell division and expansion along a major axis of leaf development. The presence of a heading allele on chromosome 7 raised the odds of heading in individual lettuce by a factor of 7.3. Using genetic complementation tests and CRISPR/Cas-9-mediated gene knockout, the authors identified the gene LsKN1, a counterpart of a maize gene implicated in meristem development, as a necessary factor for heading. In heading lettuce, LsKN1 carries a 3.9 kb-long transposon insert that elevates the gene's expression. In turn, the LsKN1 protein reduces expression of the gene LsAS1, which controls leaf dorsoventrality, resulting in heading. Analysis of 451 wild relatives of lettuce sourced from around the world suggested that the transposon insertion likely occurred after domestication, around 2,000 years ago. According to the authors, the study uncovers a genetic basis for heading, also found in commercially important vegetable crops such as endive, cabbage, and mustard.
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Article #20-19698: "Upregulation of a KN1 homolog by transposon insertion promotes leafy head development in lettuce," by Changchun Yu, Chenghuan Yan, et al.
MEDIA CONTACT: Hanhui Kuang, Huazhong Agricultural University, Wuhan, CHINA; e-mail: <kuangfile@mail.hzau.edu.cn>
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Journal
Proceedings of the National Academy of Sciences