Identification and Analysis of Genes Involved in the Jasmonate Pathway in Response to Ethephon and 1-Methylcyclopropene during the Ripening of Apple Fruit

Abstract

Fruit ripening is a complex process involving many physiological changes and the dynamic interplay between different phytohormones. In addition to ethylene, jasmonates (JAs) have also been demonstrated to play an important role in the regulation of fruit ripening. However, the mechanisms underlying the interaction between these two pathways during fruit ripening are unknown. In recent years, research has been conducted to illustrate the effects of JAs on the ethylene biosynthesis and signaling pathway, but little is known regarding the effects of ethylene on JA biosynthesis and the signaling pathway during fruit ripening. Herein, we aimed to evaluate the effects of ethylene on JA biosynthesis in ripening apple (Malus ×domestica) fruit and on the expression of key genes involved in the JA biosynthesis and the signaling pathway. For this purpose, we treated apple fruit with ethephon and 1-methylcyclopropene (1-MCP) at commercial maturity. Our data indicated that endogenous JA content and allene oxide synthase (AOS) activity were reduced by ethephon treatment at the early ripening stage, whereas they were enhanced by 1-MCP treatment at the late ripening stage. Quantitative real-time polymerase chain reaction (PCR) analysis revealed that the expression profiles of three AOS genes (MdAOS2, MdAOS3, and MdAOS5) and two lipoxygenase (LOX) genes (MdLOX22 and MdLOX28) showed similar trends with the change of AOS activity in all groups during fruit ripening. The expression of MdLOX21 and MdLOX23 was in accordance with the change of ethylene production on ripening, and it was positively regulated by ethylene, whereas the opposite effect was observed for MdLOX39 expression. The transcription of MdLOX310 and MdLOX61 appeared unaffected by ethylene during fruit ripening. Three jasmonate ZIM-domain (JAZ) genes (MdJAZ9, MdJAZ10, and MdJAZ18) were differentially upregulated by ethephon treatment whereas being downregulated by 1-MCP treatment during fruit ripening. Expression of MdJAZ13 and MdJAZ14 was downregulated at the early ripening stage by both treatments. Our results suggested regulating roles of ethylene on the JA biosynthesis and signaling pathway during fruit ripening and senescence.