Involvement of Pheophytinase in Ethylene-Mediated Chlorophyll Degradation in the Peel of Harvested 'Yali' Pear

It was recently proposed that pheophytinase (PPH) is a key protein that mediates chlorophyll (Chl) breakdown in leaves. To study the role and regulation of PPH on Chl breakdown of peel in harvested `Yali' pear (Pyrus bretschneideri Rehd. cv. `Yali') fruit, the partial sequence of PbPPH was obtained from the NCBI database, and the alignment results revealed that the amino acid sequence of PbPPH shared great similarity to PPHs of Chinese flowering cabbage (Brassica rapa var. parachinensis) and Arabidopsis (Arabidopsis thaliana), indicating that these proteins have similar functions. Ethephon treatment significantly increased ethylene production of pear fruit and accelerated the proceeding of Chl breakdown. Conversely, 1-methylcyclopropene (1-MCP) treatment decreased ethylene production and delayed Chl breakdown. PbPPH expression was closely related to the process of Chl breakdown and was correlated with the expression of Chl degradation-associated genes such as pheide a oxygenase and stay-green 1. The chlorophyllase 1 expression level was well maintained by 1-MCP treatment, whereas red Chl catabolite reductase expression was inhibited by 1-MCP. Further analysis indicated that the gene expression levels of four ethylene receptors were stimulated by ethephon and suppressed by 1-MCP treatment and that these changes were strongly correlated with Chl breakdown and similar to the expression pattern of PbPPH. These results