The involvement of papaya CpSBP1 in modulating fruit softening and carotenoid accumulation by repressing CpPME1/2 and CpPDS4

Abstract

SQUAMOSA promoter binding protein (SBP) plays important roles in many important biological processes, including fruit ripening, inflorescence branching, gibberellins signaling and flower development. Nevertheless, the transcriptional regulation mechanisms of SBPs involved in papaya fruit softening and carotenoid accumulation are still unknown. In this present study, a SBP gene, named as CpSBP1, was identified from papaya fruit. CpSBP1 was down-regulated during fruit ripening, indicating that it may be related to papaya fruit ripening at the transcriptional level. CpSBP1 was a nuclear protein and could bind to the promoters of soften-related genes CpPME1/2, as well as carotenoid biosynthesis gene CpPDS4. More importantly, CpSBP1 was a transcriptional repressor and could repress the transcriptional activities of CpPME1/2 and CpPDS4 in vivo. Collectively, these results suggest that CpSBP1 is involved in papaya fruit softening and carotenoid accumulation possibly through regulating CpPME1/2 and CpPDS4, expanding the knowledge of the regulation mechanisms of SBP transcription factor in fruit ripening.