A CHH Methylation–Ubiquitination Cascade Links Light‐Induced Anthocyanin Accumulation in Pear Fruit

Light is a key environmental cue for anthocyanin biosynthesis in fruit, but the DNA methylation targets and downstream mechanisms remain largely unclear. Using the red-skinned pear cultivar 'Aohong No. 1', we performed whole-genome bisulfite sequencing (WGBS) and RNA-seq on peels before and after light exposure following bag removal. Light-induced genome-wide CHH hypermethylation, with differentially methylated regions (DMRs) enriched in promoters. Integrative analysis identified the RING-type E3 ligase RGLG5 as a negative regulator of pigmentation. A 420-bp promoter fragment of RGLG5 underwent light-induced CHH hypermethylation, concomitant with RGLG5 transcriptional downregulation. This methylation blocked the binding of the AP2 transcription factor to the fragment, thereby silencing RGLG5. RGLG5 mediated ubiquitin-proteasome-dependent degradation of the transcription factor WRKY75L. Silencing of RGLG5 allowed WRKY75L to accumulate and directly activate MYB10, promoting pigmentation. Co-expression assays further confirmed that RGLG5 antagonized WRKY75L-driven anthocyanin accumulation in pear peel and callus tissues. Collectively, these findings support a model in which light-triggered CHH methylation of the RGLG5 promoter links epigenetic silencing to protein stability during fruit pigmentation, and identify the RGLG5 promoter as a potential epigenetic target for breeding.