Mechanism of Phloretin Accumulation in Malus hupehensis Grown at High Altitudes: Evidence from Quantitative 4D Proteomics

Phloretin is a natural dihydrochalcone (DHC) that exhibits various pharmacological and therapeutic activities. Malus hupehensis Rehd. (M. hupehensis) is widely planted in the middle of China and its leaves contain an extremely high content of phloridzin, a glycosylated derivative of phloretin. In the present study, we observed a significant increase in phloretin content in the leaves of M. hupehensis planted at high altitudes. To investigate the mechanisms of phloretin accumulation, we explored changes in the proteome profiles of M. hupehensis plants grown at various altitudes. The results showed that at high altitudes, photosynthesis- and DHC biosynthesis-related proteins were downregulated and upregulated, respectively, leading to reduced chlorophyll content and DHC accumulation in the leaves. Moreover, we identified a novel phloridzin-catalyzing glucosidase whose expression level was significantly increased in high-altitude-cultivated plants. This work provided a better understanding of the mechanism of phloretin accumulation and effective and economic strategies for phloretin production.