Gene Expression In Relationship to Volatile Biosynthesis In Apple Fruit During 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 flavor.  To better understand the regulation of volatile biosynthesis during fruit ripening and to examine the influence of ethylene on expression of volatile biosynthesis genes in fruit, apples harvested at the pre-climacteric stage were allowed to either ripen naturally or ripening was stimulated by treatment with 36 μL•L^-1 ethylene for 24. Postharvest physiological indices including respiration, ethylene production and chlorophyll fluorescence were monitored for 21 days.  Real-time qPCR was employed to investigate gene expression in relation to ethylene perception and volatile biosynthesis at day 7, 13, and 21 after treatment.  The study was repeated over two seasons.  After efficiency tests for all designed primers, 20 genes proposed to be involved in volatile biosynthesis in relation to branched amino acids and fatty acids metabolisms were selected to monitor gene expression.  Through statistical analysis, including ANOVA and principle component analysis (PCA), among the 20 volatile biosynthesis genes, 15 genes changed significantly. Genes encoding LOX, ADH3, PDC2 and malonyl-CoA:ACP transacylase increased with fruit ripening and ethylene treatment.  Ethylene treatment also induced the expression of ACAS, HPL, ACAD, ACAS, ArAT1, ECH, and ACPs as compared with control.  While ADH1 and BCAT2 were decreased by ethylene treatment.  Fruit ripening and ethylene treatment had no effect on PDC1 and ADH2. Analysis and identification of significant gene expression revealed that volatile biosynthesis, especially fatty acids biosynthesis and metabolisms in apple fruit is associated with fruit ripening and responsive to ethylene treatment.  The understanding of significant changes of these genes and their function may help to explore mechanisms controlling apple fruit ripening and their response to exogenous ethylene during ripening and senescence.