SlEAD1, an EAR motif-containing ABA down-regulated novel transcription repressor regulates ABA response in tomato

EAR motif-containing proteins are able to repress gene expression, therefore play important roles in regulating plants growth and development, plant response to environmental stimuli, as well as plant hormone signal transduction. ABA is a plant hormone that regulates abiotic stress tolerance in plants via signal transduction. ABA signaling via the PYR1/PYLs/RCARs receptors, the PP2Cs phosphatases, and SnRK2s protein kinases activates the ABF/AREB/ABI5-type bZIP transcription factors, resulting in the activation/repression of ABA response genes. However, functions of many ABA response genes remained largely unknown. We report here the identification of the ABA-responsive gene SlEAD1 (Solanum lycopersicum EAR motif-containing ABA down-regulated 1) as a novel EAR motif-containing transcription repressor gene in tomato. We found that the expression of SlEAD1 was down-regulated by ABA treatment, and SlEAD1 repressed reporter gene expression in transfected protoplasts. By using CRISPR gene editing, we generated transgene-free slead1 mutants and found that the mutants produced short roots. By using seed germination and root elongation assays, we examined ABA response of the slead1 mutants and found that ABA sensitivity in the mutants was increased. By using qRT-PCR, we further show that the expression of some of the ABA biosynthesis and signaling component genes were increased in the slead1 mutants. Taken together, our results suggest that SlEAD1 is an ABA response gene, that SlEAD1 is a novel EAR motif-containing transcription repressor, and that SlEAD1 negatively regulates ABA responses in tomato possibly by repressing the expression of some ABA biosynthesis and signaling genes.