Abstract: 【Objective】Peach (Prunus persica), a globally significant fruit and China's third most abundant deciduous fruit tree, is cherished by many. The visual appeal of peach fruits, particularly their color, is a critical factor influencing consumer purchasing decisions. Chlorophyll content is essential in determining the skin color and overall appearance of peaches, as it is closely associated with fruit maturity and quality. Despite this, the precise role of chlorophyll degradation genes within the peach genome is yet to be fully understood, and their potential effects on chlorophyll breakdown in the peach peel and fruit ripening remain unclear. This study aims to lay preliminary groundwork for understanding the ripening period and the underlying color differences in peach fruits by examining the color changes in various peach peels, the degradation process of chlorophyll, and the expression patterns of genes related to chlorophyll degradation. 【Methods】A selection of peach varieties, including Chunmei and 2-50, were chosen for this investigation. Color variations in peach fruits prior to ripening were quantified using a colorimeter, and chlorophyll content was measured with a UV spectrophotometer. While the primary chlorophyll degradation pathway has been identified, limited research exists on gene expression in fruits. To fill this gap, quantitative transcription analysis was conducted, and the coding sequences (CDS) of relevant genes were sourced from genomic databases. The expression of chlorophyll degradation-associated genes was quantified using real-time quantitative polymerase chain reaction (qRT-PCR), and the correlation between chlorophyll degradation and gene expression was established through statistical analysis. This research successfully pinpointed key factors influencing chlorophyll degradation in peach peels.【Results】The L* value of the peach fruit color difference index increased gradually from 30 to 16 days before ripening and then decreased as the fruit matured. All varieties exhibited an S-type a* value trend, with a* experiencing a sharp rise from 23 to 12 days pre-ripening. During the 12 days leading up to ripening, the green hue of the peach fruit fades, transitioning to red and causing a continuous increase in the a* value. The a* value shifts from negative to positive or nears zero from 12 to 8 days before ripening, signifying the pivotal period for color change. The b* value initially increased from 30 to 16 days before ripening and then decreased, with yellow-fleshed varieties showing higher values than white-fleshed ones. Chlorophyll content significantly decreased in all varieties as the fruit developed, with a steep decline observed between 30 and 16 days before maturity. From 12 to 8 days pre-ripening, chlorophyll levels fell below 8 µg/g across varieties, indicating visible coloring, though ripening was not complete. High expression levels of PpCLH2 and PpSGRL were detected 30 days before maturity when the fruit was entirely green. Expression levels decreased as the fruit ripened, with PpCLH1 expression peaking during the critical period of incomplete coloring and color transformation, suggesting its pivotal role in chlorophyll degradation. PpPPH, PpPAO and PpRCCR genes showed increased expression from 8 to 0 days before ripening, with PpSGR being significantly overexpressed as the fruit matured, indicating its primary role in chlorophyll degradation. Gene cluster analysis and correlation studies further highlighted the significant negative correlation between PpSGR expression and chlorophyll content, underscoring its key function during peach fruit ripening.【Conclusion】This research provides novel insights into the expression of chlorophyll degradation genes and their relationship with color change and chlorophyll content in peach peels. It identifies the period approximately 12 to 8 days before ripening as critical for color transition in peach peels, with PpCLH1 and PpSGR emerging as key genes in the pre-ripening chlorophyll degradation process. These findings not only enhance our understanding of chlorophyll degradation throughout peach fruit development but also serve as a valuable reference for future studies on the molecular mechanisms of chlorophyll degradation in peaches.
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