Overexpression of 7-hydroxymethyl Chlorophyll Reductase from Cucumber in Tobacco Accelerates Dark-Induced Chlorophyll Degradation.

7-hydroxymethyl chlorophyll (Chl) reductase (HCAR) plays critical roles in the Chl cycle and degradation during leaf senescence, however, its function in horticultural crops remains unknown. Here, we identified an gene () from cucumber ( L.) and investigated its roles in response to dark-induced Chl degradation. encoded 459 amino acids, which were orthologous to Arabidopsis HCAR, had the conserved domains, and localized in the chloroplast. Gene expression analysis showed that expression was the highest in senescent leaves and was responsive to different stresses and phytohormone treatments. Overexpression of in tobacco accelerated dark-induced Chl degradation through enhancing the expression of Chl catabolic genes. After 10 d of darkness treatment, the biomass of overexpression plants was reduced. Furthermore, the value of net photosynthetic rate, maximum quantum yield of photosystem II, and effective quantum yield of photosystem II in overexpression plants was significantly reduced in comparison to that in wild-type (WT) plants. The photosynthetic protein content, including Lhcb1, Lhcb2, Lhcb4, RbcS, and RbcL in overexpression plants exhibited a lower level as compared to that observed in WT plants. In addition, the expression of genes encoding these proteins in overexpression plants was significantly lower than that in WT plants. Moreover, overexpression plants inhibited the dark-induced accumulation of reactive oxygen species (ROS). These results indicate that affects the stability of photosynthetic proteins in chloroplasts, positively regulates Chl degradation, and plays an important role in maintaining ROS homeostasis in leaves.