The development of yellow color is an important aspect of fruit quality in yellow fleshed kiwifruit during fruit ripening, and it has a large influence on consumer preference. The yellow color is determined by carotenoid accumulation and chlorophyll degradation and is likely affected by ethylene production. This study investigates the expression of carotenoid, chlorophyll degradation, and ethylene response factors in 'Qihong' fruit, which had reached the near ripening stage (firmness ≈ 20 N) and were either left untreated (controls) or treated with 0.5 μL L-1 of 1-MCP for 12 h. Both the accumulation of β-carotene (not lutein) and degradation of chlorophyll a and b increased in response to the 1-MCP treatment, resulting in more yellow colored flesh in the 1-MCP treated fruit with higher carotenoid and lower chlorophyll contents. 1-MCP up-regulated AcLCY-β, AcSGR1, and AcPAO2, but reduced the expression of AcCCD1. These four genes were correlated with the concentrations of β-carotene and the chlorophylls. The expression of three ethylene response factors, including Acc29730, Acc25620, and Acc23763 were delayed and down-regulated in 1-MCP treated fruit, showing the highest correlation with the expression of AcLCY-β, AcSGR1, AcPAO2, and AcCCD1. Dual-Luciferase assays showed that 1-MCP treatment not only eliminated the inhibition of Acc23763 on the promoters of both AcPAO2 and AcLCY-β, but also reduced the activation of Acc29730 and Acc25620 on the AcCCD1 promoter. Our findings indicate that Acc29730, Acc25620, and Acc23763 may play an important role in the response to 1-MCP treatment during the fruit eating ripe stage, which likely altered the promoter activities of carotenoid and chlorophyll-related genes (AcPAO2, AcLCY-β and AcCCD1) to regulate their transcripts, resulting in more yellow color in the fruit flesh of 'Qihong'.
Keywords: 1-MCP; beta-carotene; chlorophyll degradation; eating ripe stage; kiwifruit.