1-Methylcyclopropene retard the yellowing of postharvest pak choi (Brassica rapa subsp. Chinensis) by regulating pigments and transcription factors during storage at 20 °C

To explore which transcription factors (TFs) modulate the pigment metabolism associated with pak choi yellowing after 1-methylcyclopropene (1-MCP) fumigation during storage at 20 °C, omics technology were carried out. 5 μL L−1 1-MCP treatment slowed the decline of total chlorophyll (Chl) contents and Chl fluorescence parameters. The total levels in carotenoid and flavonoid did not change much during storage, regardless of whether undergoing 1-MCP treatment, which might be linked to the down-regulated expression of most pigment synthesis associated genes. The bilirubin contents and its synthesis gene HO1 expression soared, which were inhibited by 1-MCP; however, the contents of bilirubin were low. The correlation analysis between Chl degradation genes and TFs revealed that BcAP2/BcERF, BcMYB, BcNACs, BcbZip, BcbHLH, BcWRKY, and BcC2H2 were the major potential TFs involved in leaf yellowing of pak choi. The numbers of TFs concerning in Chl catabolism were more than those of TFs relating to the catabolism of carotenoid and flavonoid; TFs concerning in Chl catabolism were also the most abundant TFs that respond to 1-MCP. The variation of carotenoid, flavonoid and bilirubin during storage were irrelevant to the yellowing of pak choi. BcNACs and BcWRKYs may positively regulate Chl breakdown; BcAP2/BcERFs, BcMYBs, BcbZips, BcbHLHs, and BcC2H2s may act as both transcriptional activators and repressors in Chl degradation process. Thus, 1-MCP may regulate the transcriptome expression of upstream TFs, and therefore, maintained low expression of Chl degradation associated genes, inhibited Chl degradation, helping to retard leaf yellowing of pak choi.