Gene Expression And Functional Identification Of Alcohol Acyltransferase In Melon Fruit

Muskmelon (Cucumis melo L.) is one of the major horticultural crops in the world. Aroma is an important index of its quality and one of the important factors to attract consumers and enhance the market competition In order to investigate the mechanism of ester biosynthesis and regulation, gene expression levels of AAT in developmental melon furit and fruit treated with 1-MCP,SA and ETH were analysed in this research. The antisense AAT2 gene was transformed into melon inbred line M01-3 and tomato inbred line Pr1. AAT expression level, AAT activity, growth vigor and fruit quality were determined in both wide type and transgenic plants. The aim of this research is to explore the AAT gene expression characteristics and molecular function in melon fruit development and in ester formation in fruit, and to provide the basis for improving melon quality by molecular breeding.The main results were as follows:1. Analyses of gene expression level and enzyme activity of AAT in melon fruitReal time quantitative RT-PCR results indicated that all AAT family genes studied here were specifically expressed in fruit. AAT1 and AAT2 may play a major role in ester formation in melon fruit. The expression levels of family genes were all decreased in melon fruit treated with 1-MCP. However, the expression levels of AAT family genes were induced at the different degree by ETH and SA. ETH can enhance the expression levels of AAT1, AAT2, AAT3 and AAT4, but SA only enhances the expression levels of AAT1 and AAT2.2. Transformation of antisense AAT2 gene to melonGene expression level of AAT2 in the transgenic fruit was lower than that in the control fruit. Average expression level of AAT2 in the transgenic fruit was 80% lower than that in the control fruit. The expression level of AAT2 in T0-3 fruit was the lowest, only have 12.6% that of the control. AAT activity in the transgenic fruit was also lower than that in control fruit, but the effect as not obviously as gene expression. It may be AAT is a gene family, other gene members regulate AAT activity together. The plant height of the transgenic plants was shorter than that of control plants. Reversely, the stem diameter of the transgenic plants was much thinner than that of control plants. The net photosynthetic rate of transgenic plants was slightly slower than that of control plants throughout plant development.3. Transformation of antisense AAT2 gene to tomatoSPME-GCMS analysis showed that the contents of 3-Methyl butanol,Hexanol,Hexanal and Cis-3-hexenol were reduced in transgenic tomato fruits than those in the control fruit. The real-time quantitative RT-PCR results showed that expression level of AAT2 had the same trend in both the transgenic fruit and the control fruit. But, the mRNA levels of AAT2 gene in transgenic fruits reduced obviously comparing to the control fruit during fruit development. Transgenic plants were distinctly weaker than control plants. Vc content in the transgenic fruit decreased 17.39% than that of the control fruit.