A ripening-associated ethylene response factor ERF.D7 activates ARF2 orthologs to regulate tomato fruit ripening

Abstract

Despite the obligatory nature of ethylene to climacteric fruit ripening and the identification of 77 Ethylene Response Factors (ERFs) in the tomato genome, the role of only limited ERFs has been validated in the ripening process. Here, using a comprehensive morpho-physiological, molecular and biochemical approach, we demonstrate the regulatory role of SlERF.D7 in tomato fruit ripening. The expression of SlERF.D7 positively responds to exogenous ethylene and auxin treatments, most likely in a RIN-independent manner. Overexpression of SlERF.D7 promotes ripening and its silencing has the opposite effects. Alterations in its expression modulated ethylene production, pigment accumulation, and fruit firmness. Consistently, genes involved in ethylene biosynthesis and signalling, lycopene biosynthesis, and cell wall loosening were upregulated in the overexpression lines and downregulated in RNAi lines. These transgenic lines also accumulated altered levels of IAA at late-breaker stages. A positive correlation between ARF2 orthologs transcripts and SlERF.D7 mRNA levels and the fact that ARF2A and ARF2B are direct targets of SlERF.D7 underpinned the perturbed auxin-ethylene crosstalk for the altered ripening program observed in the transgenic fruits. Overall, this study uncovers that SlERF.D7 positively regulates SlARF2A/B abundance to amalgamate auxin and ethylene signalling pathways for controlling tomato fruit ripening. HighlightThe present study identifies a new ripening regulator, SlERF.D7, that controls tomato fruit ripening by activating other known-ripening regulators, SlARF2A and SlARF2B.