Résumé
The ubiquity of nonparental hybrid phenotypes, such as hybrid vigor and
hybrid inferiority, has interested biologists for over a century and is of
considerable agricultural importance. Although examples of both phenomena
have been subject to intense investigation, no general model for the
molecular basis of nonadditive genetic variance has emerged, and
prediction of hybrid phenotypes from parental information continues to be
a challenge. Here we explore the genetics of hybrid phenotype in 435
Arabidopsis thaliana individuals derived from intercrosses of 30 parents
in a half diallel mating scheme. We find that nonadditive genetic effects
are a major component of genetic variation in this population and that the
genetic basis of hybrid phenotype can be mapped using genome-wide
association (GWA) techniques. Significant loci together can explain as
much as 20% of phenotypic variation in the surveyed population and include
examples that have both classical dominant and overdominant effects. One
candidate region inherited dominantly in the half diallel contains the
gene for the MADS-box transcription factor AGAMOUS-LIKE 50 (AGL50), which
we show directly to alter flowering time in the predicted manner. Our
study not only illustrates the promise of GWA approaches to dissect the
genetic architecture underpinning hybrid performance but also demonstrates
the contribution of classical dominance to genetic variance.