Two papaya MYB proteins function in fruit ripening by regulating some genes involved in cell-wall degradation and carotenoid biosynthesis.

Abstract

MYB transcription factors (TFs) are common in plants and play important functions in growth and development, including fruit development and ripening. However, the role of MYB proteins in papaya ripening (fruit ripening and carotenoid biosynthesis) remains unclear. Two MYB genes were cloned from papaya pulp. They were named CpMYB1 (MYB44-like) and CpMYB2, and belong to the S22 subgroup of the R2R3-MYB family. Their expression levels decreased during fruit ripening. Subcellular localization analysis showed that both CpMYB1 and CpMYB2 were nuclear proteins, indicating that they might function in the nucleus. Moreover, CpMYB1 and CpMYB2 could bind to the promoters of cell-wall degradation genes (CpPME1, CpPME2, and CpPG5) and carotenoid biosynthesis genes (CpPDS2, CpPDS4, and CpCHY-b). Further research found that both CpMYB1 and CpMYB2 were transcriptional repressors, and they could suppress the activities of the promoters of CpPME1, CpPME2, CpPG5, CpPDS2, CpPDS4, and CpCHY-b. These results indicated that MYB TFs CpMYB1 and CpMYB2 might have a function in papaya fruit softening and carotenoid accumulation by regulating cell-wall degradation and carotenoid biosynthesis related genes, which provide a new view about the role of MYB TFs in fruit ripening. © 2020 Society of Chemical Industry.