Calcium and reactive oxygen species metabolism regulate anthocyanin accumulation in ‘Xinqihong’ pear fruit

Peel color is one of the main characteristics of pear fruit sensory quality, which directly affects the commercial value of pear fruit. Red pears are favored by many consumers because of their bright appearance. Fruit peel fading before ripening is a common problem during the growth of red pears, such as ‘Xinli 7’ fruit (Pyrus bretschneideri). ‘Xinqihong’ (P. bretschneideri) is a bud mutation of ‘Xinli 7’ pear, and its production area and yield are increasing due to the excellent features of red peel color stability. However, the regulatory mechanisms underlying red peel color stability during ripening in ‘Xinqihong’ pear have not been elucidated. In this study, we found that the contents of anthocyanin and calcium in the peel of ‘Xinqihong’ pear were significantly higher than those in ‘Xinli 7’ before the ripening stage. Moreover, the present study found that PbCaM7 could regulate red peel color stability in ‘Xinqihong’ fruit. The relative expression level of PbCaM7.1 in the peel of ‘Xinqihong’ was significantly positively correlated with anthocyanin content. The result of the GUS staining assay showed that light up-regulated the activity of the PbCaM7.1 gene promoter. Overexpression of PbCaM7.1 in pear peel stimulated anthocyanin accumulation and consequently promoted red peel formation. In addition, the contents of O2− and H2O2 in the peel of ‘Xinqihong’ fruit were markedly higher than those in ‘Xinli 7’ fruit at 127 d after full bloom, which was attributed to the transcriptional regulation of reactive oxygen species metabolic genes. The results of in this study suggest that red peel color stability in ‘Xinqihong’ pear during ripening is closely associated with calcium signaling and reactive oxygen species metabolism, which will provide new insights into exploring the regulatory mechanisms of red peel color stability in pear fruit.