1-Methylcyclopropene (1-MCP) treatment differentially mediated expression of vacuolar processing enzyme (VPE) genes and delayed programmed cell death (PCD) during ripening and senescence of apple fruit

Abstract

• 1-MCP reduced VPE activity and delayed vacuolar-mediated PCD in apple fruit. • MdVPE s had varying expression patterns in response to 1-MCP during ripening. • MdVPE s were differentially expressed after transient over-expression of MdERF2. The main purpose of this research was to evaluate the impacts of 1-methylcyclopropene (1-MCP) treatment on vacuolar processing enzyme ( VPE ) genes and programmed cell death (PCD) during ripening and senescence of apple fruit ( Malus × domestica Borkh.). The ethylene antagonists 1-MCP (1 μL L −1 ) was applied to apples after harvest. Both treated and control fruit were stored at 20 ± 2°C. The data showed that 1-MCP treatment maintained flesh firmness, delayed climacteric peaks of respiration and ethylene, reduced VPE activity, relative electrical conductivity (REC), malondialdehyde (MDA) content and reactive oxygen species (ROS) accumulation during ripening. Transmission electron microscopy (TEM) and DNA ladder assay revealed that 1-MCP delayed vacuolar-mediated PCD in ripening apple fruit. Generally, expression of MdVPEγ1, MdVPEγ2, MdVPEδ4 and MdVPEδ7 was down-regulated by 1-MCP treatment, while expression of MdVPEα4 and MdVPEβ2 was enhanced by it during ripening compared with controls. 1-MCP treatment differentially reduced expression of MdVPEα1, MdVPEα2 and MdVPEα5 at the early ripening stage but promoted their expression at the late ripening stage, while it had the opposite effects on MdVPEβ1, MdVPEβ3 and MdVPEγ4 expression. After transient overexpression of MdERF2, MdVPEs displayed varying expression patterns, among which MdVPEα2 transcripts increased greater than the other genes. Our results indicated that MdVPEs expression and vacuolar-mediated PCD were mediated by ethylene signal during ripening and senescence of apple fruit.