Molecular identification of genes controlling flowering time, maturity, and photoperiod response in soybean

Most plants activate the developmental transition from the vegetative to the reproductive phase in response to photoperiod length, temperature, and other environmental stimuli. Successful identification of major genes underlying flowering time and maturity in soybean is a prerequisite for understanding of the regulation of flowering time. Recent progress has been made toward molecular bases of soybean maturity loci by using both candidate gene and positional cloning approaches. In particular, successful identification of the molecular identity of the soybean maturity locus E1 is a remarkable achievement, because this gene is essential for understanding the regulation of flowering time and maturity in soybean. The E1 gene has a putative bipartite nuclear localization signal, and a domain distantly related to B3. Transcriptional profiling showed the E1 gene is under photoperiodic regulation. The E2 gene in soybean encodes GmGIa, a homolog of Arabidopsis GIGANTEA that has multiple functions involved in the circadian clock and flowering. Both of the E3 and E4 genes encode copies of PHYTOCHROME A proteins, and both genes response differentially to light with different red to far-red quantum (R:FR) ratios. In addition, two homologs (GmFT2a and GmFT5a) of FLOWERING LOCUS T coordinately promote photoperiodic flowering in soybean. Public availability of the soybean genome sequence to the research community will greatly facilitate fine mapping and cloning of more genes underlying flowering time and photoperiodic response. Further research on identified genes will help us to understand the exquisite regulatory network of parallel and intertwining pathways controlling flowering time and photoperiodic response in soybean.