Anthocyanin accumulation differences in European pears caused by Phytochrome-interacting factor 3 (PcPIF3) promoter mutations under UV-B.

The phenomenon of red fading in late-stage red-skinned pear fruit development significantly impacts its value. This phenomenon also occurs in 'Starkrimson', albeit to a lesser extent compared to 'Red Bartlett' and other varieties. The reasons for the differences in anthocyanin accumulation during the late stages of fruit development in red-skinned European pears varieties are not yet understood. Here, we report a novel pattern of anthocyanin accumulation in response to UV-B in 'Starkrimson' pears, which is associated with mutations in the PcPIF3 promoter. Through transcriptome analysis of 'Red Bartlett' and 'Starkrimson' pears, we identified the differentially expressed gene PcPIF3, which is capable of promoting anthocyanin biosynthesis through direct binding to the promoter region of PcMYB10. Under moderate UV-B conditions, the 'Starkrimson' PcPIF3 were significantly increased. By analyzing the PcPIF3 promoter regions of different red-skinned pear varieties, we identified the differential binding element as W-BOX 1 and subsequently screened for the upstream positive regulator, PcWRKY11. Y1H and related experiments demonstrated that under UV-B exposure, PcWRKY11 binds specifically to the W-BOX 1 element in the 'Starkrimson' PcPIF3 promoter, thereby enhancing its transcription. These findings indicate that PcWRKY11, in response to UV-B, interacts with the W-BOX 1 element in the 'Starkrimson' PcPIF3 promoter, promoting anthocyanin biosynthesis and mitigating the fading of red coloration in 'Starkrimson' pears. The difference in the PcWRKY11-PcPIF3 module represents a novel mechanism for the variation in anthocyanin accumulation among different red-skinned pear varieties.