1-Methylcyclopropene retards pak choi (Brassica rapa subsp. chinensis) yellowing via BcNAC055-, BcMYB44- and BcOBF1-mediated regulation of the key chlorophyll degrading gene BcNYC1 during storage at 20 °C

The objective of this study was to investigate the molecule regulatory mechanism of 1-MCP treatment on leaf yellowing of pak choi during storage at 20 °C. In the present study, compared with control and 10 μL L -1 ethylene-treated pak choi, 5.0 μL L -1 1-MCP fumigation alleviated the yellowing process of pak choi as proved by the maintenance of higher level of colour, chlorophyll content and appearance. 1-MCP treatment decreased chlorophyll breakdown by down-regulating the activity of chlorophyll-degrading enzymes (chlorophyll b reductase CBR and pheophytinase PPH) and expression of their related genes (BcNYC1 and BcPPH). The application of 1-MCP also inhibited the transcript abundant of ethylene biosynthesis and signal transduction genes (BcACO, BcEIN3 and BcERF), reduced ethylene production, thus helping to keep green colour of pak choi; however, ethylene treatment exerted an opposite function. Meanwhile, three transcription factors BcNAC055, BcMYB44, and BcOBF1 were successfully cloned. Experiments performed using yeast one-hybrid assay, dual-luciferase reporter system and in vivo biolumines-cence imaging assay, confirmed that BcNAC055, BcMYB44, and BcOBF1 directly bound to the BcNYC1 promoter. 1-MCP inhibited the expression levels of BcNAC055, BcMYB44, BcOBF1, and BcNYC1 during storage, while the application of ethylene activated their expression. In conclusion, 1-MCP down-regulated the expression of chlorophyll degradation key genes BcNYC1 via inhibiting the transcript level of its three positively regulators (BcNAC055, BcMYB44, and BcOBF1), lowed the activity of chlorophyll-degrading enzyme CBR, thereby helping mitigate chlorophyll breakdown to retard leaf yellowing in pak choi. The results of this work extend our understanding of 1-MCP-delayed yellowing in postharvest pak choi.