Lewis Ramsey S, Drake-Stowe Katherine E, Heim Crystal, Steede Tyler, Smith William, Dewey Ralph E
Department of Crop and Soil Sciences, North Carolina State University, Raleigh, NC, United States.
Front Plant Sci. 2020 Apr 3;11:368. doi: 10.3389/fpls.2020.00368. eCollection 2020.
Genetic methodologies for reducing nicotine accumulation in the tobacco plant ( L.) are of interest because of potential future regulations that could mandate lowering of this alkaloid in conventional cigarettes. Inactivation of tobacco genes such as the () gene family believed to encode for enzymes involved in one of the latter steps of nicotine biosynthesis could be a viable strategy for producing new tobacco cultivars with ultra-low leaf nicotine accumulation. We introduced deleterious mutations generated via ethyl methanesulfonate treatment of seed or gene editing into six known members of the gene family and assembled them in different combinations to assess their relative contribution to nicotine accumulation. Significant reductions (up to 17-fold) in percent leaf nicotine were observed in genotypes homozygous for combined mutations in , , and . The addition of mutations in , , and had no additional significant effect on lowering of nicotine levels in the genetic background studied. Reduced nicotine levels were associated with reductions in cured leaf yields (up to 29%) and cured leaf quality (up to 15%), evidence of physiological complexities within the tobacco plant related to the nicotine biosynthetic pathway. Further nicotine reductions were observed for a mutant line cultivated under a modified production regime in which apical inflorescences were not removed, but at the expense of further yield reductions. Plants in which mutations were combined with naturally occurring recessive alleles at the and loci exhibited further reductions in percent nicotine, but no plant produced immeasurable levels of this alkaloid. Findings may suggest the existence of a minor, alternative pathway for nicotine biosynthesis in . The described genetic materials may be of value for the manufacture of cigarettes with reduced nicotine levels and for future studies to better understand the molecular biology of alkaloid accumulation in tobacco.
由于未来可能出台的法规要求降低传统香烟中这种生物碱的含量，因此降低烟草植株中尼古丁积累的遗传方法备受关注。烟草基因如被认为编码参与尼古丁生物合成后期步骤之一的酶的（）基因家族的失活，可能是培育具有超低叶片尼古丁积累的新烟草品种的可行策略。我们将通过甲磺酸乙酯处理种子或基因编辑产生的有害突变引入到该基因家族的六个已知成员中，并以不同组合进行组装，以评估它们对尼古丁积累的相对贡献。在、和组合突变的纯合基因型中，观察到叶片尼古丁百分比显著降低（高达17倍）。在研究的遗传背景中，、和突变的添加对降低尼古丁水平没有额外的显著影响。尼古丁水平的降低与烤后叶片产量降低（高达29%）和烤后叶片质量降低（高达15%）相关，这证明了烟草植株内与尼古丁生物合成途径相关的生理复杂性。在一种改良的生产模式下种植的突变系观察到尼古丁进一步降低，在这种模式下顶生花序未被去除，但代价是产量进一步降低。在、位点处突变与自然存在的隐性等位基因相结合的植株，尼古丁百分比进一步降低，但没有植株产生不可测量水平的这种生物碱。研究结果可能表明在中存在一条次要的、替代的尼古丁生物合成途径。所描述的遗传材料对于制造尼古丁含量降低的香烟以及未来更好地理解烟草中生物碱积累的分子生物学研究可能具有价值。
