Expression of NAC6 Transcription Factor and Its Impact on Carotenoid Metabolism in Postharvest Mango Fruit

The NAC transcription factors play an important regulatory role in plant growth and development. In order to explore the impact of NAC6 on carotenoid metabolism in postharvest mango fruit, this study investigated changes in the carotenoid contents as well as the expression of NAC6 and key enzymes involved in carotenoid synthesis and metabolism in the mature peel and pulp of 2 mango varieties, “Tainong” and “Jinhuang”, at commercial maturity, during postharvest storage under constant temperature (20 ℃), constant humidity (85%), and dark conditions. The results showed that both mango varieties contained α-carotene, lutein, β-carotene, β-cryptoxanthin, and zeaxanthin. Throughout the storage process, the expression of NAC6 in both mango varieties showed a continuous upward trend, reaching a peak in the late stage of storage, followed by a slight decline. Correlation analysis showed that NAC6 might induce the gene expression of 1-deoxy-D-xylulose-5-phosphate reductoisomerase, farnesyl pyrophosphate synthase, geranylgeranyl pyrophosphate synthase, phytoene synthase, phytoene desaturase, ζ-carotene desaturase, carotenoid isomerase, β-carotene hydroxylase, and violaxanthin de-epoxidase in mango fruit, while inhibiting the gene expression of lycopene β-cyclase, neoxanthin synthase, and 9-cis-epoxycarotenoid dioxygenase. The expression of NAC6 in the peel and pulp of “Tainong” mango was significantly negatively correlated with the gene expression of carotenoid cleavage dioxygenase (CCD), with correlation coefficients of −0.841 0 and −0.838 3, respectively. NAC6 might delay the degradation of carotenoids by inhibiting the expression of CCD. The results from this research provide an experimental basis for the postharvest storage and preservation of mango fruit as well as its quality control.