Department of Genetics, University of Wisconsin-Madison, Madison, WI, USA.
PLoS Genet. 2013 Jun;9(6):e1003604. doi: 10.1371/journal.pgen.1003604. Epub 2013 Jun 27.
A reduction in number and an increase in size of inflorescences is a common aspect of plant domestication. When maize was domesticated from teosinte, the number and arrangement of ears changed dramatically. Teosinte has long lateral branches that bear multiple small ears at their nodes and tassels at their tips. Maize has much shorter lateral branches that are tipped by a single large ear with no additional ears at the branch nodes. To investigate the genetic basis of this difference in prolificacy (the number of ears on a plant), we performed a genome-wide QTL scan. A large effect QTL for prolificacy (prol1.1) was detected on the short arm of chromosome 1 in a location that has previously been shown to influence multiple domestication traits. We fine-mapped prol1.1 to a 2.7 kb "causative region" upstream of the grassy tillers1 (gt1) gene, which encodes a homeodomain leucine zipper transcription factor. Tissue in situ hybridizations reveal that the maize allele of prol1.1 is associated with up-regulation of gt1 expression in the nodal plexus. Given that maize does not initiate secondary ear buds, the expression of gt1 in the nodal plexus in maize may suppress their initiation. Population genetic analyses indicate positive selection on the maize allele of prol1.1, causing a partial sweep that fixed the maize allele throughout most of domesticated maize. This work shows how a subtle cis-regulatory change in tissue specific gene expression altered plant architecture in a way that improved the harvestability of maize.
花序数量减少和大小增加是植物驯化的一个常见方面。玉米由类蜀黍驯化而来，其穗数和排列方式发生了显著变化。类蜀黍有长的侧枝，在节点上有多个小穗，在顶端有雄穗。玉米的侧枝短得多，顶端有一个大穗，没有在侧枝节点上有额外的小穗。为了研究这种生殖力（植物上的穗数）差异的遗传基础，我们进行了全基因组 QTL 扫描。在 1 号染色体短臂上发现了一个大的生殖力效应 QTL（prol1.1），其位置先前已被证明影响多个驯化性状。我们将 prol1.1 精细定位到位于 grassy tillers1（gt1）基因上游的 2.7kb“致病区域”，该基因编码一个 homeodomain leucine zipper 转录因子。组织原位杂交显示，prol1.1 的玉米等位基因与 gt1 在节点丛中的表达上调有关。由于玉米不会启动次生耳芽，gt1 在玉米节点丛中的表达可能会抑制它们的启动。群体遗传分析表明，prol1.1 的玉米等位基因受到了正选择，导致了一个部分清除，使玉米等位基因在大多数驯化玉米中固定下来。这项工作表明，组织特异性基因表达的细微顺式调控变化如何以一种提高玉米可收获性的方式改变了植物的结构。
