The SlDOF3.4-SlCDF4 module improves tomato growth under low-nitrogen conditions

DNA-binding with one finger (DOF) proteins are plant-specific transcription factors (TFs) that play critical roles in plant growth and development, including nitrogen metabolism, but the roles of these TFs in the nitrogen response of tomato (Solanum lycopersicum) remain largely unexplored. Here, we show that overexpressing the DOF gene SlDOF3.4 enhanced the growth of tomato seedlings under low nitrogen (LN) conditions, resulting in longer roots and greater biomass accumulation. Multiple assays demonstrated that SlDOF3.4 interacts with another DOF family member, SlCDF4, and that both TFs bind to the promoters of the N-assimilation gene Glutamine synthetase (SlGS) and the jasmonic acid (JA) biosynthesis gene Lipoxygenase (SlLOXD), suggesting that SlDOF3.4 and SlCDF4 cooperatively regulate nitrogen assimilation and JA biosynthesis. In support of this notion, co-expressing SlCDF4 and SlDOF3.4 enhanced the binding activity of SlDOF3.4 to the SlGS and SlLOXD promoters in a dual-luciferase reporter assay. Under LN conditions, genes related to nitrogen assimilation and JA biosynthesis were markedly upregulated in SlDOF3.4-overexpressing and SlCDF4-overexpressing tomato plants. Knockout of SlCDF4 impaired plant growth under LN conditions, a phenotype that was partially alleviated by treatment with methyl jasmonate. These results provide insight into the roles of DOF TFs in nitrogen assimilation and JA biosynthesis in crops.