Abstract
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.
Highlights
The ‘‘domestication syndrome’’ of crop plants is a suite of adaptive traits that arose in response to direct and indirect selection pressures during the domestication process [1,2,3]
Among the changes in maize from its ancestor, teosinte, was a switch from 100 or more small ears per plant in teosinte to just one or two large ears in maize. We show that this change in ear number has a relatively simple genetic architecture involving a gene of large effect, called grassy tillers1
We show that grassy tillers1 experienced a tissue-specific gain in expression in maize that is associated with suppressing the initiation of multiple ears per plant such that only one or two large ears are formed
Summary
The ‘‘domestication syndrome’’ of crop plants is a suite of adaptive traits that arose in response to direct and indirect selection pressures during the domestication process [1,2,3] This suite of traits includes an increase seed or fruit size, larger inflorescences, an increase in apical dominance, more determinate growth and flowering, loss of natural seed dispersal, loss of seed dormancy, and, in some cases, the gain of self-compatibility. These traits make crop plants easier to cultivate and harvest, resulting in increased value for human use. The fewer but larger inflorescences mature in a narrower window of time, enabling all the fruit/seed of a plant to be harvested at the same time of optimal maturation
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