Upregulation of a homolog by transposon insertion promotes leafy head development in lettuce.

Leafy head is a unique type of plant architecture found in some vegetable crops, with leaves bending inward to form a compact head. The genetic and molecular mechanisms underlying leafy head in vegetables remain poorly understood. We genetically fine-mapped and cloned a major quantitative trait locus controlling heading in lettuce. The candidate gene () is a homolog of () from Complementation and CRISPR/Cas9 knockout experiments confirmed the role of in heading. In heading lettuce, there is a CACTA-like transposon inserted into the first exon of (▽). The transposon sequences act as a promoter rather than an enhancer and drive high expression of ▽. The enhanced expression of ▽ is necessary but not sufficient for heading in lettuce. Data from ChIP-sequencing, electrophoretic mobility shift assays, and dual luciferase assays indicate that the LsKN1▽ protein binds the promoter of and down-regulates its expression to alter leaf dorsoventrality. This study provides insight into plant leaf development and will be useful for studies on heading in other vegetable crops.