Abstract
BackgroundIn plants, CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) is a key negative regulator in photoperiod response. However, the biological function of COP1-interacting protein 1 (CIP1) and the regulatory mechanism of the CIP1-COP1 interaction are not fully understood.ResultsHere, we identified the apple MdCIP1 gene based on the Arabidopsis AtCIP1 gene. Expression pattern analysis showed that MdCIP1 was constitutively expressed in various tissues of apple, and responded to stress and hormone signals at the transcriptional level. Ectopic expression of MdCIP1 complemented the phenotypes of the Arabidopsis cip1 mutant, and MdCIP1 inhibited anthocyanin biosynthesis in apple calli. In addition, the biochemical assay demonstrated that MdCIP1 could interact with MdCOP1 protein by their coiled-coil domain, and MdCIP1-OX/cop1–4 had a similar phenotype in photomorphogenesis with the cop1–4 mutant, suggesting that COP1 is epistatic to CIP1. Furthermore, the transient transformation assay indicated that MdCIP1 repressed anthocyanin biosynthesis in an MdCOP1-mediated pathway.ConclusionTake together, this study finds that MdCIP1 acts as a repressor in regulating hypocotyl elongation and anthocyanin biosynthesis through MdCOP1 in apple.
Highlights
In plants, CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) is a key negative regulator in photoperiod response
COP1 is transported into the nucleus under dark conditions, regulates the seedlings to skotomorphogenesis by degrading the photomorphogenesis promoters LONG HYPOCOTYL IN FAR-RED 1 (HFR1), LONG AFTER FAR-RED LIGHT 1 (LAF1) and ELONGATED HYPOCOTYL 5 (HY5); under light conditions, COP1 is located in the cytoplasm, promotes biosynthesis of the downstream substrate, which promotes photomorphogenesis [12,13,14]
After Simple modular architecture research tool (SMART) analysis of protein secondary structure, MdCIP1 contains a potential coiled-coil domain, corresponding to aa 251– 684 of the full length MdCIP1, which is analogous to AtCIP1 (Fig. S1b)
Summary
Protein structure of MdCIP1 The apple MdCIP1 (MDP0000230486) gene was blasted from the database Apple Genome V1.0 Predicted Peptides by using the protein sequence of Arabidopsis. The response of MdCIP1 to ABA is faster than salt and PEG treatment, reaching the maximum after 6 h treatment (Fig. 1f) These results indicate that MdCIP1 can respond to stress and hormone signals at the transcriptional level. Ectopic overexpression of MdCIP1 in the cop mutant showed a similar phenotype of hypocotyl with that of cop, no matter the light or dark treatments (Fig. 5). MdCIP1-OX/cop fully exhibited the features of cop, dwarfing and branching (Fig. S6) This result indicates that COP1 is epistatic to CIP1. MdCOP1 negatively regulate anthocyanin biosynthesis and the peel coloration of apple fruits by ubiquitination degradation of the MdMYB1 protein [50]. Anthocyanin biosynthesis by hormonal and environmental signals, providing a new perspective on the hormonal and environmental impact on fruit coloration
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