Lskipk Lsatpase double mutants are necessary and sufficient for the compact plant architecture of butterhead lettuce

Abstract

Abstract Lettuce, an important leafy vegetable crop worldwide, has rich variations in plant architecture. Butterhead lettuce, a popular horticulture type, has a unique plant architecture with a loose leafy head. The genetic and molecular mechanisms for such a compact plant architecture remain unclear. In this study, we constructed a segregating population through crossing a butterhead cultivar and a stem lettuce cultivar. Genetic analysis identified the LsKIPK gene, which encodes a kinase, as the candidate gene controlling butterhead plant architecture. The Lskipk gene in the butterhead parent had a nonsense mutation, leading to a partial predicted protein. CRISPR/Cas9 and complementation tests verified its functions on plant architecture. We showed that the loss-of-function of LsKIPK is necessary but not sufficient for the butterhead plant architecture. To identify additional gene required for butterhead lettuce, we crossed a butterhead cultivar and a crisphead cultivar, both with the mutated Lskipk gene. Genetic mapping identified a new gene encoding a ATPase contributing to butterhead plant architecture. Knockout and complementation tests showed that the loss-of-function of LsATPase is also required for the development of butterhead plant architecture. Lskipk Lsatpase double mutants could reduce leaf size and leaf angle, leading to butterhead plant architecture. Expression and cytology analysis indicated that the loss-of-function of LsKIPK and LsATPase contributed to butterhead plant architecture by regulating cell wall development, a regulatory mechanism different from that for crisphead. This study provides new gene resources and theory for the breeding of crop ideotype.