NAC transcription factors SNAC4 and SNAC9 synergistically regulate tomato fruit ripening by affecting expression of genes involved in ethylene and abscisic acid metabolism and signal transduction

•SNAC4/9 can regulate tomato fruit ripening.•SNAC4/9 can interact with key genes of ABA and ethylene at the protein level.•SNAC4 regulates the promoter of ABA, ethylene key genes upstream.•SNAC4/9-ABA-ethylene constitutes a regulatory network for tomato fruit ripening. NAC (NAM, ATF1/2 and CUC2) is a transcription factor that can regulate many physiological and biochemical reactions in plants. Two NAC genes, SNAC4 (NM_001279348.2) and SNAC9 (NM_001365397.1), with similar secondary structures have been isolated from tomato (Solanum lycopersicum L.). The pattern of SNAC4/9 co-regulation of tomato ripening with abscisic acid (ABA) and ethylene through yeast two-hybrid and bimolecular fluorescence complementation assays has revealed that SNAC4/9 can interact with genes related to ABA and ethylene (SAPK3, SlPYL9, SlAREB1, SlACS2 and SlACO1) at the protein level. Electrophoretic mobility shift assay and yeast one-hybrid showed that SNAC4, but not SNAC9, acts directly on the promoter regions of SAPK3, SlCYP707A1, SlACS8 and SlACO6 and can activates them. In addition, quantitative real-time PCR analyses of SNAC4/9-silenced fruit obtained by virus-induced gene silencing, and phytohormone-treated fruit, confirmed that the interaction genes are regulated by SNAC4/9 and thereby affect fruit ripening. In summary, we found that SNAC4/9 can regulate fruit ripening by positively acting on key genes in the synthesis and signal transduction of ABA and ethylene. SNAC4/9 cooperates with these phytohormones as part of the tomato fruit ripening regulatory network.