4 For example, KIX8 (KINASE-INDUCIBLE DOMAIN INTERACTING 8) and KIX9 repress leaf growth via function as adaptor proteins for the co-repressor TOPLESS, 5 OFP1 (Ovate family protein 1) regulates cell elongation via repressing the expression of GA20ox1 ( Gibberellin 20-oxidase 1), 6 TOE1 (TARGET OF EARLY ACTIVATION TAGGED (EAT) 1) and TOE2 regulate flowering via repressing the expression of FT ( FLOWERING LOCUS T), 7 whereas several repressor ERFs such as ERF4 and ERF7 are involved in the regulation of plant responses to stresses. 4ĮAR motif-containing proteins are able to function as transcription repressors or recruit co-repressors to repress gene expression, therefore play important roles in regulating plants growth and development, as well as plant response to environmental stimuli. 2 EAR motif-proteins mediated transcriptional repression has been considered to be the main form of transcriptional repression in plants, 3 and a genome wide searching of LxLxL or DLNxxP sequence-containing proteins have identified more than 20,000 EAR motif-containing proteins from 71 different plant species. 1 Based on sequence comparison of the EAR motifs in class II ERFs, C2H2 family proteins, and some other EAR motif-containing proteins, the consen sus sequence patterns of EAR motifs were further refined as LxLxL and DLNxxP. The EAR (ERF-associated amphiphilic repression) motifs, which contain a conserved sequence pattern of (L/F)DLN(L/F)xP, were initially identified in the class II ERFs (Ethylene-responsive factors) and some C2H2 family proteins, and have been shown to confer transcriptional repression activities. 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. 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. 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 CRISPR gene editing, we generated transgene-free slead1 mutants and found that the mutants produced short roots. We found that the expression of SlEAD1 was down-regulated by ABA treatment, and SlEAD1 repressed reporter gene expression in transfected protoplasts.
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. However, functions of many ABA response genes remained largely unknown.
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. ABA is a plant hormone that regulates abiotic stress tolerance in plants via signal transduction. 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.
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