LAUSR

Lettuce (Lactuca sativa) is one of the most popular vegetables worldwide. Diverse leaf shapes, including wavy leaves, are important traits for lettuce. We dissected the genetics of wavy leaves using an F2 segregating population of lettuce. A major QTL controlling wavy leaves was identified. The candidate region contains the LsKN1 gene, which was previously shown to be indispensable for leafy heads in lettuce. Complementation test and knockout experiments verified the function of LsKN1 on wavy leaves. The LsKN1 allele, which has the insertion of a transposon and controls leafy head in a previous population, promotes wavy leaves in the current population. Occasional transposition of the CACTA transposon from the LsKN1 gene compromised its function on wavy leaves. High expression of the LsKN1 gene upregulates several key genes associated with cytokinin (CK) to increase its contents in leaves. In contrast, high expression of the LsKN1 gene downregulates the expression of genes in the gibberellin (GA) biosynthesis pathway to decrease GA contents in leaves. Application of CK on leaves increased wavy phenotype, while application of GA dramatically flattened the leaves. We conclude that high expression of the LsKN1 gene increases CK contents but decreases GA contents in leaves, switches determinate cells to indeterminate, and consequently leads to wavy leaves.