Genetic and molecular bases of photoperiod responses of flowering in soybean

Abstract

Flowering is one of the most important processes involved in crop adaptation and productivity. A number of major genes and quantitative trait loci (QTLs) for flowering have been reported in soybean (Glycine max). These genes and QTLs interact with one another and with the environment to greatly influence not only flowering and maturity but also plant morphology, final yield, and stress tolerance. The information available on the soybean genome sequence and on the molecular bases of flowering in Arabidopsis will undoubtedly facilitate the molecular dissection of flowering in soybean. Here, we review the present status of our understanding of the genetic and molecular mechanisms of flowering in soybean. We also discuss our identification of orthologs of Arabidopsis flowering genes from among the 46,367 genes annotated in the publicly available soybean genome database Phytozome Glyma 1.0. We emphasize the usefulness of a combined approach including QTL analysis, fine mapping, and use of candidate gene information from model plant species in genetic and molecular studies of soybean flowering.

Keywords: flowering; maturity gene; photoperiod sensitivity; soybean.

Fig. 1

Syntenic blocks containing soybean orthologs of Arabidopsis flowering genes in homoeologous regions of different chromosomes. The orthologs, represented by Arabidopsis gene symbols, are shown in their positions on the soybean physical maps. The orthologs within each set of syntenic blocks are arranged in the same order, but the blocks are sometimes inverted relative to one another. st and en indicate start and end of chromosome, respectively.

Fig. 2

Genetic and physical maps of SSR markers tagging three flowering-time QTLs detected in the cross between Misuzudaizu and Moshido Gong 503, and soybean orthologs of Arabidopsis flowering genes predicted in the delineated regions. Distance along the vertical bars indicates the physical distance reported in the Phytozome database. The genetic distance (cM) shown to the left of each SSR marker is cited from an integrated soybean map (Song et al. 2004) and represents the distance from the end of linkage group to the marker. Dotted lines indicate the possible positions of QTLs inferred from the closest flanking DNA markers (Watanabe et al. 2004, Yamanaka et al. 2005). Small white squares indicate genomic regions delineated by fine mapping, each containing a single soybean ortholog of an Arabidopsis flowering gene. These regions were subjected to further analyses to identify the genes underlying qFT2 and qFT3 (Watanabe et al. 2009, 2011). Orthologs of flowering genes with underlines indicate genes corresponding to the QTL (shown to the left).