Expression Analysis Of Gene And Preliminary Mapping Of Major QTL Related To Parthenocarpy Of Cucumber

Cucumber (Cucumis sativus L.) is Cucurbitaceae Cucumis vegetable crops. It’s one of the world’s top ten vegetable crops. According to the Food and Agriculture Organization of the United Nations (FAO) statistics in2011, the cucumber production was47.36million tons in China, the output value reached＄9.1billion, much higher than the other countries of the world. Parthenocarpy is one of the most important goal characters during cucumber breeding. To understand parthenocarpic mechanism of cucumber, we research about parthenocarpy through gene transcription and molecular markers.1. Identification and Characterization of Cytokinin Biosynthetic Gene CsIPTs in CucumberTo identify IPT family genes in cucumber(Cucumis sativus L.) and investigate the relationship between cucumber fruit development and CsIPT, parthenocarpic line’EC1’ and non-parthenocarpic line’8419s-l’were used for real-time RT-PCR analyses. Based on the expression patterns of CsIPT in different organs, functional genes involved in fruit development were identified and further analyzed by their expression patterns during fruit development. The results indicated that similarity of eight CsIPT genes were in the range of17.3%-33.2%, length of amino acids were280-504AA. CsIPTs had a common ATP/GTP binding domain of the [(A, G)-X4-G-K-(S, T)]. CsIPT4contained a putative zinc finger-like motif (C-X2-C-X12,18-H-X5-H). CsIPT3, CsIPT5, CsIPT7and CsIPT8had higher expression in the early cucumber fruit. In the undeveloped fruit CsIPTl, CsIPT3, CsIPT4and CsIPT5showed a significant increasing trend. CsIPT2and CsIPT8were related to fruit development after pollination, at the same time the expression of CsIPT2was higher in the early fruit development of ’EC1’. Therefore, it was speculated that CsIPT2may participate in the regulation of fruit development in cucumber parthenocarpic line. 2. Cloning and Characterization of Isopentenyl-transferases Gene (CsIPT2) in CucumberTo analyze the role of CsIPT2genes during fruit development of cucumber (Cucumis sativus L.) and response after different hormones treatment, based on cloning and sequence analysis of CsIPT2gene, then parthenocarpic line ’EC1’ and non-parthenocarpic line ’8419s-1’ were used for real-time RT-PCR analyses. The results showed that the length of CsIPT2gene was843bp, encoded280amino acids. The protein structure model was extremely similar to IPT protein of hop (Humulus lupulus L.). The expression of gene was higher during the fruit development of cucumber after pollination. At the same time the expression of CsIPT2was higher in the early of natural and late of artificially induced parthenocarpic fruit. Therefore, it was speculated that CsIPT2may play an important role in promoting parthenocarpy of cucumber. Moreover, the five hormones (GA, ET,6-BA, ABA and NAA) were able to up-regulation expression of the gene. The highest expression of ET、6-BA、ABA and NAA appeared6h after treatment, while only GA did3h after treatment. The expression of the gene increased along with the NAA concentration became higher and higher.3. Preliminary Mapping of Major QTL Related to Parthenocarpy of CucumberTo map QTL for parthenocarpy in cucumber, we have constructed F2family used parthenocarpy inbred lines ’ECl’ and non-parthenocarpy inbred lines ’8419s-1’. The results of SPSS analysis indicated the level of parthenocarpy we got was accord with normal distribution. Based on the cucumber genetic map containing82polymorphic markers, a QTL was detected on chromosome2. It explained42.56%of phenotypic variance. The results would be beneficial for further studying on the parthenocarpy in cucumber, as well as molecular marker-assisted selection breeding.