为探讨bHLH转录因子家族成员MYC2b基因与烟叶中烟碱含量及烟碱含量杂种优势表现的相关性，利用RT-qPCR分析NtMYC2b基因与烟碱合成途径关键酶基因的表达，测定烟碱含量和烟碱杂种优势表现。结果表明，移栽后80 d，NtMYC2b在烟草亲本GDH88和巴斯玛根部的表达量较移栽后66 d上调，其根和叶中烟碱含量增加，杂交种根中NtMYC2b、鸟氨酸脱羧酶基因（ODC）、精氨酸脱羧酶基因（ADC）、N-甲基转移酶基因（PMT）、N-甲基腐胺氧化酶基因（MPO）的表达量相对于亲本平均表达量均明显上调，且除MPO外，NtMYC2b与ODC、ADC、PMT、QPT(喹啉酸磷酸核糖转移酶基因)在强优势组合VA116×巴斯玛中的相对表达量均明显高于弱优势组合VA116×GDH88，根和叶中烟碱含量及其杂种优势表现也具有相同的趋势，表明NtMYC2b参与了烟碱的合成，还可能参与了烟碱含量杂种优势的形成。相关性分析表明，在亲本根部，NtMYC2b表达量与PMT表达量呈显著正相关；在杂交种根部，NtMYC2b表达量与ADC、MPO表达量呈显著正相关；在杂交种叶片中，NtMYC2b表达量与烟碱含量杂种优势呈显著正相关，PMT表达量与ODC、ADC表达量均呈显著正相关。关键酶基因启动子序列分析表明，ADC中含有1个MYC结合位点和1个G-box元件；PMT中含有7个MYC结合位点和1个G-box元件。推测NtMYC2b可能通过与ADC、PMT的顺式元件MYC结合位点或G-box元件特异性结合调控ADC、PMT的表达，进而促进烟碱的合成，且NtMYC2b还参与了烟碱含量杂种优势的形成。

To investigate the correlation between transcription factor MYC2b and nicotine content and its heterosis in tobacco,ＲT-qPCＲ was used to analyze the expression of NtMYC2b and key enzyme genes in the nicotine synthesis pathway,and the nicotine content and its heterosis in roots and leaves of tobacco were determinated.The results showed that the expression of NtMYC2b in parent roots(GDH88 and Bas ma) was upregulated at 80 d compared with 66 d after transplanting,and their nicotine content in root and leaves was also increased.The expressions of NtMYC2b,ornithine decarboxylase gene(ODC),arginine de carboxylase gene(ADC) ,putrescine-N-methyltransferase gene (PMT) and N-methylputrescine oxidase gene(MPO) were significantly upregulated in root of hybrid relative to their parents.The relative expres sion levels of NtMYC2b,ODC,ADC,PMT and QPT(quinoline phosphoribosyltransferase gene) in the strong heterosis combination(VA116 × Basma) were significantly higher than those in the weak heterosis combination(VA116 × GDH88) ,meanwhile,the nicotine content and its heterosis also showed the same trend in roots and leaves of hybrid.It indicated that NtMYC2b was involved in the synthesis of nicotine and might also be involved in the formation of heterosis of nicotine content.Correlation analysis showed that the expression of NtMYC2b was significantly positively correlated with PMT in the parent roots,the same with ADC and MPO in hybrid roots.Moreover,between NtMYC2b expression and nicotinic content heterosis,between PMT expression and ODC and ADC expression,was also a significant positive correla tion in hybrid leaves.Sequence analysis showed that the promoter sequence of ADC contained 1 MYC binding site and 1 G-box element,the promoter sequence of PMT contained 7 MYC binding sites and 1 G box element.Therefore,it is speculated that NtMYC2b may regulate the expression of ADC and PMT by specifically binding with cis-element MYC binding site or G-box elementto promote the synthesis of nico tine.These findings suggest that NtMYC2b is involved in the synthesis of nicotine and the formation of het erosis in nicotine content．