Solanum lycopersicum CLASS-II KNOXgenes regulate fruit anatomy via gibberellin-dependent and independent pathways

The pericarp is the predominant tissue determining the structural characteristics of most fruits. However, the molecular and genetic mechanisms controlling pericarp development remain only partially understood. Previous studies have identified that CLASS-II KNOX genes regulate fruit size, shape, and maturation inArabidopsis thalianaandSolanum lycopersicum. Here we characterized the roles of theSolanum lycopersicumCLASS-II KNOX (TKN-II) genes in pericarp development via a detailed histological, anatomical, and karyotype analysis of theTKN-IIknockdown (35S:amiR-TKN-II) fruits. We identify that35S:amiR-TKN-IIpericarps contain more cells around their equatorial perimeter and fewer cell layers than the control. In addition, the cell sizes but not the ploidy levels of these pericarps were dramatically reduced.Further, we demonstrate that fruit shape and pericarp layer number phenotypes of the35S:amiR-TKN-IIfruits can be overridden by theproceramutant, known to induce a constitutive response to the plant hormone gibberellin. However, neither theproceramutation nor exogenous gibberellin application can fully rescue the reduced pericarp width and cell size phenotype of35S:amiR-TKN-IIpericarps. Our findings establish that TKN-II genes regulate tomato fruit anatomy, acting via gibberellin to control fruit shape but utilizing a gibberellin-independent pathway to control the size of pericarp cells.HighlightTomatoCLASS-II KNOXgenes regulate fruit and pericarp anatomy via GA-dependent and independent pathways.