Involvement of BcERF109 in 1-MCP-delayed yellowing of pak choi (Brassica rapa subsp. Chinensis) via mitigation of major chlorophyll-degrading gene expression during storage

Leaf yellowing is a typical senescence symptom in postharvest pak choi (Brassica rapa subsp. Chinensis). Ethylene response factors (ERFs) are considered important regulators of leaf senescence. This study explored the likely regulatory effects of BcERF on pak choi yellowing via 1-methylcyclopropene (1-MCP) treatments. We identified an ERF transcription factor (TF), BcERF109, which may be involved in ethylene-induced pak choi yellowing. Treatment with 5.0 µL L–1 1-MCP suppressed the transcripts of chlorophyll catabolism genes (BcPPH1, BcRCCR, BcSGR2, and BcNYC1), inhibited decreases in chlorophyll content and chlorophyll fluorescence parameters, delayed chloroplast disintegration, and eventually mitigated yellowing. The treatment also blocked ethylene production and impeded the activities and transcripts of ethylene synthesis enzymes (ACC oxidase [ACO] and 1-aminocyclopropene-1-carboxylate [ACC] synthase [ACS]). In contrast, treatment with 10.0 µL L–1 ethylene accelerated pak choi yellowing, as indicated by greater ethylene production, activities and transcripts of ACO and ACS, and expression of chlorophyll catabolism genes, as well as reductions in chlorophyll content and fluorescence parameters. BcERF109 was identified as a nuclear-localised protein; its transcription levels were downregulated by 1-MCP and upregulated by ethylene. Molecular biology assays revealed that BcERF109 enhanced the transcriptional capacities of BcPPH1, BcRCCR, BcNYC1, and BcSGR2 by binding to their promoters. The transient overexpressing of BcERF109 in tobacco leaves stimulated the expression of endogenous genes (BcPPH1, BcRCCR, BcNYC1, BcSGR2, and BcERF109), leading to accelerated chlorophyll degradation and leaf yellowing. The application of 1-MCP mitigated pak choi yellowing by influencing ethylene synthesis and modulating the regulatory effects of BcERF019 on genes associated with chlorophyll catabolism. These results revealed a new regulatory mechanism involving ERF TFs in 1-MCP-induced delayed yellowing of green vegetables.