Map-based Cloning And Functional Analysis Of EI (Elongated Internode) Gene In Tomato

Internode length,as an important factor of plant architecture,has been paid more and more attention in tomato breeding.However,there is little information on the internode length of tomato.In this study,the elongated internode mutant P502,derived from the natural mutant of inbred line 05T606,was analyzed.The genetic law of the elongated internode was conducted by six populations.The F₂populations constructed by Heinz 1706×P502 were used to fine mapping the EI（Elongated Internode）gene.The function of the EI gene was confirmed by overexpression experiment.Our study provided a theoretical basis for revealing the regulation network of internode length in tomato and possible technical support for genetic improvement of tomato plant architecture.The main results are as follows:1.The elongated internode mutant P502 showed longer internode in the whole seedlings than wild type05T606,and each internode was elongated significantly.Cytology observation showed that internode elongation of P502 is associated with the longitudinal elongation cells.The mutant P502 has higher bioactive GAs concentration,compared with the wild type 05T606,and responds to exogenous GA₃ and PAC,indicating the P502 is a GA-sensitive mutant.2.Six populations（P₁,P₂,F₁,B₁,B₂,and F₂）were obtained from the Heinz 1706（normal internode）×P502（long internode）and P1609（short internode）×P502 crosses,respectively.The elongated internode trait is QTL and a multi-generation joint analysis of major genes plus polygene model showed that internode elongation was regulated by main gene.Moreover,the heritabilities of major genes were higher in F₂ and B₂ generation,which ranged from 52.11%to 78.16%.3.The F₂ obtained by Heinz 1706 and P502 were used for BSA and QTL analysis,the result showed the ei was located on chromosome 2 and there was a major QTL,which explained 73.6%phenotypic variation.By fine mapping,the ei was narrowed down to 75.8-kb between CAPS17and InDel6.After analyzing ten genes in the candidate interval,it was found that only one base difference（G-T）existed in the coding region of Solyc02g080120.1.Amino acid sequence alignment showed the base mutation（G-T）in mutant P502 caused amino acid（G-V）variation in the conserved domain PcbC family.Solyc02g080120.1 encodes GA2ox7（SlGA2ox7）,which is GA degrading enzyme,was located in the nucleus and endoplasmic reticulum.After over-expression complementary experiment,transgenic plants showed dwarf with shorter internode.4.The expression of the EI gene is organ-specific.The mutation of EI gene did not significantly affect its transcriptional level,however,the expression levels of genes which were involved in the GA metabolic pathway were upregulated.