The Genetic Architecture of Maize Flowering Time
Codifying Maize Modifications Maize, one of our most important crop species, has been the target of genetic investigation and experimentation for more than 100 years. Crossing two inbred lines tends to result in "better" offspring, in a process known as heterosis. Attempts to map the genetic loci that control traits important for farming have been made, but few have been successful (see the Perspective by Mackay) Buckler et al. (p. 714) and McMullen et al. (p. 737) produced a genomic map of maize that relates recombination to genome structure. Even tremendous adaptations in very diverse species were produced by numerous, small additive steps. Differences in flowering time in maize among inbred lines were not caused by a few genes with large effects, but by the cumulative effects of numerous quantitative trait loci each of which has only a small impact on the trait. Assaying nearly one million plants reveals that maize flowering time is not controlled by a large effect at any single locus. Flowering time is a complex trait that controls adaptation of plants to their local environment in the outcrossing species Zea mays (maize) We dissected variation for flowering time with a set of 5000 recombinant inbred lines (maize Nested Association Mapping population, NAM) Nearly a million plants were assayed in eight environments but showed no evidence for any single large effect quantitative trait loci (QTLs) Instead, we identified evidence for numerous small effect QTLs shared among families; however, allelic effects differ across founder lines. We identified no individual QTLs at which allelic effects are determined by geographic origin or large effects for epistasis or environmental interactions. Thus, a simple additive model accurately predicts flowering time for maize, in contrast to the genetic architecture observed in the selfing plant species rice and Arabidopsis.
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