VvEIL2 and VvEIL4 regulate ethylene synthesis and carotenoid metabolism during senescence of grape rachis

To understand the mechanisms underlying rachis browning and how to delay post-harvest rachis senescence, ‘Shine Muscat’ grape clusters were treated by 1-methylcyclopropene before cold storage. Rachis browning index, ethylene production, and carotenoid content were determined, and the transcriptome of rachis and the regulation of VvEIL2 and VvEIL4 were explored. The results indicated that 1-MCP treatment inhibited rachis browning, and ethylene production and carotenoid content were decreased in the rachis compared to the control in the 2nd week of storage. Transcriptome analysis showed that carotenoid synthesis and lysine degradation pathways were the most enriched during rachis senescence. Transient over-expression of VvEIL4 in ‘Thompson Seedless’ grape leaves induced VvACS5, VvACO2, and VvERF95 expression and ethylene production. Both VvEIL4 and VvERF95 could activate VvACS5 and VvACO2 promoters. Transient over-expression of VvEIL2 in grape leaves decreased the transcript levels of key genes in carotenoid metabolism. Dual-luciferase assays further verified the activation of the VvCrtISO promoter by VvEIL2 was inhibited. These results suggested that VvEIL2 and VvEIL4 regulate ethylene synthesis and carotenoid metabolism during the senescence of grape rachis.