Abstract
BackgroundPearl millet landraces display an important variation in their cycle duration. This diversity contributes to the stability of crop production in the Sahel despite inter-annual rainfall fluctuation. Conservation of phenological diversity is important for the future of pearl millet improvement and sustainable use. Identification of genes contributing to flowering time variation is therefore relevant. In this study we focused on three flowering candidate genes, PgHd3a, PgDwarf8 and PgPHYC. We tested for signatures of past selective events within polymorphism patterns of these three genes that could have been associated with pearl millet domestication and/or landraces differentiation. In order to implement ad hoc neutrality tests, a plausible demographic history of pearl millet domestication was inferred through Approximate Bayesian Computation by using eight neutral STS loci.ResultsDomesticated pearl millet exhibited 84% of the nucleotide diversity level found in the wild population. No specific polymorphisms were found either in the wild or in the domestic populations. The Bayesian approach and previous studies suggest that gene flow between wild relatives and domesticated pearl millets is a main factor explaining these results. Early and late landraces did not show significant genetic differentiation at both the neutral and the candidate loci. A positive selection was evidenced in PgHd3a and PgDwarf8 genes of domestic forms but not in the wild population.ConclusionOur results strongly suggest that PgHd3a and PgDwarf8 were likely targeted by selection during domestication. However, a potential role of any of the three candidate genes in the phenological differentiation between early and late landraces was not supported by our data. Reasons why these results contrast with previous results that have shown a slight but significant association between PgPHYC polymorphisms and variation in flowering time in pearl millet are discussed.
Highlights
Plant domestication is often considered as a two step evolutionary process
Among the traits usually considered as targets of this second step of the domestication process, cycle length has been crucial for domestic populations to cope with new environmental conditions encountered during the expansion of the cultivation areas [4,5]
There is an important variation in flowering time within each group of landraces [9], we have recently shown, in a case study, that the distribution of flowering times among early and late landraces are clearly distinct [11]
Summary
The first step corresponds to the evolution of characteristic traits of domestic phenotypes under the selective pressures that have occurred under the conditions of cultivation of wild populations by the first farmers, as early as the beginning of the domestication [1]. The second step, concerns the diversification of the domestic gene pool as a byproduct of local adaptations to new environments and to human needs and tastes This further evolution has produced the morphological and physiological diversity of the domestic gene pool which largely exceeds what is usually observed in their wild counterparts. Pearl millet landraces display an important variation in their cycle duration This diversity contributes to the stability of crop production in the Sahel despite inter-annual rainfall fluctuation. In order to implement ad hoc neutrality tests, a plausible demographic history of pearl millet domestication was inferred through Approximate Bayesian Computation by using eight neutral STS loci
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