Date Published:

Abstract:

Compound leaves are composed of multiple separate blade units termed leaflets. In tomato (Solanum lycopersicum) compound leaves, auxin promotes both leaflet initiation and blade expansion. However, it is unclear how these two developmental processes interact. With highly variable complexity, tomato compound leaves provide an ideal system to address this question. In this study, we obtained and analyzed mutants of theWUSCHEL-RELATED HOMEOBOX(WOX) family geneSlLAM1from tomato, whose orthologs in tobacco (Nicotiana sylvestris) and other species are indispensable for blade expansion. We show thatSlLAM1is expressed in the middle and marginal domains of leaves, and is required for blade expansion in leaflets. We demonstrate thatsllam1mutants cause a delay of leaflet initiation and slightly alter the arrangement of first-order leaflets, whereas the overall leaflet number is comparable to that of wild-type leaves. Analysis of the genetic interactions betweenSlLAM1and key auxin signaling components revealed an epistatic effect ofSlLAM1in determining the final leaf form. Finally, we show thatSlLAM1is also required for floral organ growth and affects the fertility of gametophytes. Our data suggest thatSlLAM1promotes blade expansion in multiple leaf types, and leaflet initiation can be largely uncoupled from blade expansion during compound leaf morphogenesis.