Vann Laura, Kono Thomas, Pyhäjärvi Tanja, Hufford Matthew B, Ross-Ibarra Jeffrey
Department of Plant Sciences, University of California , Davis, CA , USA.
Department of Plant Sciences, University of California , Davis, CA , USA ; Department of Agronomy and Plant Genetics, University of Minnesota , Twin Cities, Minneapolis, MN , USA.
PeerJ. 2015 Apr 16;3:e900. doi: 10.7717/peerj.900. eCollection 2015.
The teosinte branched1(tb1) gene is a major QTL controlling branching differences between maize and its wild progenitor, teosinte. The insertion of a transposable element (Hopscotch) upstream of tb1 is known to enhance the gene's expression, causing reduced tillering in maize. Observations of the maize tb1 allele in teosinte and estimates of an insertion age of the Hopscotch that predates domestication led us to investigate its prevalence and potential role in teosinte. We assessed the prevalence of the Hopscotch element across an Americas-wide sample of 837 maize and teosinte individuals using a co-dominant PCR assay. Additionally, we calculated population genetic summaries using sequence data from a subset of individuals from four teosinte populations and collected phenotypic data using seed from a single teosinte population where Hopscotch was found segregating at high frequency. Genotyping results indicate the Hopscotch element is found in a number of teosinte populations and linkage disequilibrium near tb1 does not support recent introgression from maize. Population genetic signatures are consistent with selection on the tb1 locus, revealing a potential ecological role, but a greenhouse experiment does not detect a strong association between the Hopscotch and tillering in teosinte. Our findings suggest the role of Hopscotch differs between maize and teosinte. Future work should assess tb1 expression levels in teosinte with and without the Hopscotch and more comprehensively phenotype teosinte to assess the ecological significance of the Hopscotch insertion and, more broadly, the tb1 locus in teosinte.
玉米分枝1（tb1）基因是控制玉米与其野生祖先大刍草之间分枝差异的一个主要数量性状基因座。已知在tb1上游插入一个转座元件（跳房子元件）会增强该基因的表达，导致玉米分蘖减少。对大刍草中玉米tb1等位基因的观察以及对驯化前跳房子元件插入年龄的估计，促使我们研究其在大刍草中的普遍性及其潜在作用。我们使用共显性聚合酶链反应（PCR）分析法，评估了来自美洲的837个玉米和大刍草个体样本中跳房子元件的普遍性。此外，我们利用来自四个大刍草种群的部分个体的序列数据计算了群体遗传学总结，并利用在一个发现跳房子元件高频分离的单一的大刍草种群的种子收集了表型数据。基因分型结果表明，在一些大刍草种群中发现了跳房子元件，并且tb1附近的连锁不平衡不支持近期来自玉米的基因渗入。群体遗传学特征与tb1基因座上的选择一致，揭示了一种潜在的生态作用，但温室实验未检测到跳房子元件与大刍草分蘖之间有强烈关联。我们的研究结果表明，跳房子元件在玉米和大刍草中的作用有所不同。未来的工作应该评估有和没有跳房子元件的大刍草中tb1的表达水平，并更全面地对大刍草进行表型分析，以评估跳房子元件插入以及更广泛地说大刍草中tb1基因座的生态意义。
