Abstract
BackgroundFlowering time is a domestication trait of Glycine max and varies in soybeans, yet, a gene for flowering time variation has not been associated with soybean domestication. GIGANTEA (GI) is a major gene involved in the control of flowering time in Arabidopsis, although three GI homologs complicate this model in the soybean genome.ResultsIn the present work, we revealed that the geographic evolution of the GIGANTEAa (GIa) haplotypes in G. max (GmGIa) and Glycine soja (GsGIa). Three GIa haplotypes (H1, H2, and H3) were found among cultivated soybeans and their wild relatives, yet an additional 44 diverse haplotypes were observed in wild soybeans. H1 had a premature stop codon in the 10th exon, whereas the other haplotypes encoded full-length GIa protein isoforms. In both wild-type and cultivated soybeans, H2 was present in the Southern region of China, and H3 was restricted to areas near the Northeast region of China. H1 was genetically derived from H2, and it was dominant and widely distributed among cultivated soybeans, whereas in wild populations, the ortholog of this domesticated haplotype H1 was only found in Yellow River basin with a low frequency. Moreover, this mutated GIa haplotype significantly correlated with early flowering. We further determined that the differences in gene expression of the three GmGIa haplotypes were not correlated to flowering time variations in cultivated soybeans. However, only the truncated GmGIa H1 could partially rescue gi-2 Arabidopsis from delayed flowering in transgenic plants, whereas both GmGIa H2 and H3 haplotypes could significantly repress flowering in transgenic Arabidopsis with a wild-type background.ConclusionsThus, GmGIa haplotype diversification may have contributed to flowering time adaptation that facilitated the radiation of domesticated soybeans. In light of the evolution of the GIa gene, soybean domestication history for an early flowering phenotype is discussed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0653-9) contains supplementary material, which is available to authorized users.
Highlights
Flowering time is a domestication trait of Glycine max and varies in soybeans, yet, a gene for flowering time variation has not been associated with soybean domestication
These results suggest that flowering time is a key domestication trait for soybean fecundity
We found that H1 is a rare haplotype in wild soybeans restricted to the Yellow River region in China, yet it is highly abundant in many cultivated soybean accessions from all detected geographic subgroups, suggesting that soybean domestication may have occurred in the Yellow River region
Summary
Flowering time is a domestication trait of Glycine max and varies in soybeans, yet, a gene for flowering time variation has not been associated with soybean domestication. The transition from vegetative to reproductive growth is an important developmental process in plants, and flowering time is controlled by the merger of complex networks including the photoperiod, vernalization, gibberellin, autonomy, and age pathway [1, 2]. These regulatory networks respond to endogenous cues and the external environment to maximize reproduction, flowering time is an important agronomic trait. It acts as a floral activator in Pisum sativum (LATE BLOOMER1), Triticum aestivum (TaGI1) and Hordeum vulgare (HvGI) [15,16,17], whereas it functions as a floral repressor in Oryza sativa (OsGI) and soybean (GmGI) [18,19,20]
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