Ethylene Perception and Biosynthesis In Apple Fruit Is Differentially Controlled by Ethylene During Fruit Ripening and Senescence

Apple fruit (Malus domestica Barkh) is a well known climacteric fruit and a good model to study fruit ripening and senescence.  Ethylene plays an important role in regulating fruit ripening and senescence and directly influences the development of the eating quality of fresh apples, including appearance, color, texture, and flavour.  Two studies were conducted.  In the first study, apple fruit were harvested at the pre-climacteric stage and allowed to naturally ripen or ripening was stimulated by treatment with 36 μL•L^-1 ethylene for 24 h. In the second study, fruit were harvested also at pre-climacteric similar stages and treated with 1-MCP treatment (1 μL•L^-1 for 24 h). Postharvest physiological indices, ethylene production and chlorophyll fluorescence were monitored up to 21 d after ethylene treatment or up to 47 d after 1-MCP treatment.  Real-time qPCR was employed to investigate gene expression in relation to ethylene perception and biosynthesis at day 0, 7, 13, and 21 for ethylene treatment and day7, 14, 22, 39, and 43 for 1-MCP treatment.  Each study was repeated over two seasons.  After efficiency tests for all designed primers, 22 genes were selected to monitor gene expression in relation to ethylene perception and biosynthesis.   Through statistical analysis, including ANOVA and principle component analysis (PCA), 14 genes were found to change significantly.  Genes encoding ACS1, ACS2, ACO1, and the ETR1, ETR2, ERS1, ERS2, ERF1, and ERF2 genes were significantly up-regulated in fruit during ripening and after ethylene treatment.  EIN3, ETR5, and CTR1-5 genes were increased with ethylene treatment. In contrast, ACO3 and EIN2B seemed to be decreased. While the ACS3, EIN2, EIN2A as well as CTR1-1, CTR1-2, and CTR1-4 genes were unchanged. 1-MCP treatment showed the opposite effect of ethylene, while reduced ETR1, CTRs and EIN2A. These results provide additional evidence that regulation of these genes expression is under the influence of ethylene.  Analysis and identification of significant gene expression revealed that ethylene biosynthesis and perception during apple fruit ripening and senescence is associated with fruit ripening and responsive to treatment of ethylene or its action inhibitor.  This study demonstrated the complexity and dynamic changes of transcriptional profiles of ethylene perception and biosynthesis.  The understanding of significant changes of these genes and their functions may help to explore mechanisms controlling apple fruit ripening and their response to ethylene during ripening and senescence.