Cloning And Expression Analysis Of FT Homology Genes In Allium Cepa

Onion (Allium cepa L.) is a biennial herb belong to Liliaceae Allium, it was well known as "Vegetables queen" because of its strong effect on nutrition value and health function. According to the statistics, China is one of the largest onion producer in the word. However, early bolting becomes a important problem which could affect the yield and quality of onion no matter in the northern long sunshine time area where has a cultivation pattern that seedling in spring and harvest in autumn or the short sunshine time area where has the pattern as winter cultivation in central plains and southwest. FLOWERING LOCUS T(FT), originally cloned in arabidopsis, is not only one of the key genes regulating plants flowering during the process of photoperiodic response in flowering plants but also one of the important factor for flowering. Thus, the cloning of onion FT gene and realizing of its expression pattern can enrich the mechanism for onion flowering and prov-ide reference for regulating plants flowering through the genetic engineering means.In this study, The four florigen gene isolated from Allium cepa line’1007’by RT-PCR and Rapid Amplification of cDNA Ends,and predicted their protein structure, analyzed the FT gene expression patterns in different organs during different periods by real time quantitative PCR.The main results are following:(1) The four florigen gene which designated as AcFTl (KF913629)、AcFT2(KF864664.1)、AcFT3(KF994783.1.1) and AcLFT (KF864665.1) isolated from Allium cepa line,’1007’by RT-PCR and Rapid Amplification of cDNA Ends.The full-length sequence of AcFT1、AcFT2and AcFT3was791bp,the length of5"the untranslation region and3’untranslated region were37bp and220bp, full-length of ORF sequence was534bp and encoded177amino acid,molecule-ar weight was19.8kD,isoelectric point was7.89; The length of AcLFT gene was838bp,5’non translation region was37bp,3’non translation region was261bp,ORF sequence was540bp and encoded a179amino acid sequence, molecular weight was20.1kD,isoelectric point was8.81.(2) The homology among the four FT homologous genes was analyzed by DNAMAN software, it indicated that the similarity in AcFTl,AcFT2and AcFT3was very high and the homology of amino acid sequence was98.3%;AcFT2and AcFT3amino acid homology was96.6%;the amino acid homology in AcLFT with AcFT1,AcFT2,AcFT3was84.7%,83.1%and83.6%respectively. (3) Compared and analyzed4FT homologous genes of Allium cepa with the FT gene of logged plants in the GeneBank,the results showed that AcFTl,AcFT2and AcFT3with had over96%with Allium fistulosum AfFT homologous genes,the homology between AcLFT and AfFT was84.4%;amino acid homology in the onion amino acid sequence of AcLFT、AcFT1、AcFT2and AcFT3with apple,wheat,papaya,cucumber,cymbidium,longan and arabidopsis thaliana were63.0%to84.0%,it also demonstrated that the FT gene was still relatively conservative in the long-term evolution process. Phylogenetic analysis showed that it was closest between Allium cepa and Allium fistulosum, According to clustering analysis of FT amino acid,the latter divide monocotyledon and dicotyledon into the two coordinate branches.(4) According to the cloning cDNA sequence above,specific primers were designed and DNA sequences were obtained after PCR amplification in Allium cepa. The sequencing results showed that the DNA sequence of AcFTs and AcLFT were534bp and540bp,consistent with the corresponding cDNA sequence and the sequence without introns.(5) The analysis for AcFTs and AcLFT expression patterns by fluorescent quantitative PCR declared that AcFTs and AcLFT were expressed at different growth stages of organ,and the expression reached the maximum quantity in the leaves from vernalization to bolt,suggesting that floral genes were expressed abundantly in leaves before bolting.