Anthocyanins, as natural pigments belonging to the flavonoid group, play a crucial role in plant reproduction, stress resistance and human fitness. Kiwifruit, which is rich in anthocyanins, demonstrates significant potential for promoting health benefits. Although light is widely recognized as an inducer of anthocyanin accumulation, we observed that kiwifruit accumulates more anthocyanin after bagging treatment. This unexpected finding suggests that anthocyanin biosynthesis in kiwifruit may also be regulated by other environmental or physiological factors influenced by bagging, such as humidity, temperature, or gas exchange. This implies that bagging may trigger specific regulatory pathways that promote anthocyanin accumulation through multiple environmental cues beyond light. Therefore, RNA-seq was performed to find the potential pathway. A total of 260 differentially expressed genes were found, including 8 transcription factors and 1 anthocyanin biosynthesis gene F3GT1 (glucosyltransferase). Dual-luciferase reporter assays revealed that bHLH transcription factors could activate the promoter of F3GT1 by 2.45-fold. We infer that bagging treatment increases the kiwifruit anthocyanin content through the bHLH291-F3GT1 pathway. This study not only highlights the potential agricultural applications and commercial value of bagging treatment but also provides new theoretical support for improving fruit coloration and optimizing breeding strategies.

Background: Plant leaves often develop red coloration in response to aging and environmental changes. High light or continuous light treatments can elevate anthocyanins, which we observed in normally green kiwifruit leaves. Methods and results: The underlying mechanism in this response was investigated using transcriptomic analysis. Results revealed that multiple anthocyanin biosynthesis genes, particularly Flavonoid-3-O-glucosyltransferase ( AcF3GT1a ), ( AcF3GT4 ) can convert unstable anthocyanidins into stable colored anthocyanins, and glutathione-S-transferase ( AcGST1 ) is responsible for the safe delivery of anthocyanins from the endoplasmic reticulum to the vacuole, were significantly upregulated under continuous light light-stress treatments. AcMYB210 , a member of the S6 MYB subfamily in kiwifruit with previously unknown function, was specifically induced. Dual-luciferase, yeast one-hybrid, and homologous genetic transformation assays confirmed that AcMYB210 directly binds to and activates the promoters of anthocyanin pathway genes, thereby promoting anthocyanin accumulation in kiwifruit leaves. A light-induced transcription factor, AcWRKY22 , was found to directly bind and activate the AcMYB210 promoter. In addition, AcMYB210 was highly expressed in plants whose leaves turned red after waterlogging stress. Conclusions: In summary, our data reveal the critical role of the AcWRKY22-AcMYB210 module in mediating light signal regulation of anthocyanin biosynthesis in kiwifruit leaves, providing new insights into the regulation of kiwifruit anthocyanin biosynthesis by light signals.