Dissection of the domestication-shaped genetic architectureof lettuce primary metabolism

Lettuce (Lactuca sativa L.) is an important vegetable crop species worldwide. The primary metabolism ofthis species is essential for its growth, development and reproduction as well as providing a considerabledirect source of energy and nutrition for humans. Here, through investigating 77 primary metabolites in 189accessions including all major horticultural types and wild lettuceL. serriolawe showed that the metabo-lites inL. serriolawere different from those in cultivated lettuce. The findings were consistent with thedemographic model of lettuce and supported a single domestication event for this species. Selection signalsamong these metabolic traits were detected. Specifically, galactinol, malate, quinate and threonate weresignificantly affected by the domestication process and cultivar differentiation of lettuce. Galactinol and raf-finose might have been selected during stem lettuce cultivation as an adaption to the local environments inChina. Furthermore, we identified 154 loci significantly associated with the level of 51 primary metabolites.Three genes (LG8749721,LG8763094andLG5482522) responsible for the levels of galactinol, raffinose, qui-nate and chlorogenic acid were further dissected, which may have been the target of domestication and/oraffected by local adaptation. Additionally, our findings strongly suggest that human selection resulted inreduced quinate and chlorogenic acid levels in cultivated lettuce. Our study thus provides beneficial geneticresources for lettuce quality improvement and sheds light on the domestication and evolution of this impor-tant leafy green.