Proposed model of the genetic network comprising three maturity genes and one growth-habit gene affecting pre- and post-flowering photoperiod responses in soybean under LD. A) Photoperiod-sensitive plants with E1 or e1-as and either E3 or E4. PHYA-regulated E1 expression inhibits the expression of soybean orthologs of FT (GmFT2a and GmFT5a). Once induced by brief exposure to SD, flowering persists after the transfer to LD, but seed maturation and stem termination are inhibited under the control of PHYA encoded by the E3 and E4 alleles through activation of an unknown factor (Y) and upregulation of Dt1 expression, respectively. B) Photoperiod-insensitive plants of the e3/e4 group. Owing to the dysfunction of PHYA, flowering is induced under LD, which is followed by normal seed maturation and stem termination. C and D) Photoperiod-insensitive plants of C) the e1/E3/e4 or e1/e3/E4 group and D) the e1-as/e3/E4 group. In the e1/E3/e4 or e1/e3/E4 group, flowering is induced by the dysfunction of the E1 gene (panel C); whereas that in the e1-as/e3/E4 group is induced through an unknown factor (X) (panel D). Seed maturation of plants in these two groups is delayed similarly because of the presence of the E3 or E4 allele. However, stem growth after LD terminates earlier in the e1/E3/e4 or e1/e3/E4 group than in the e1-as/e3/E4 group: PHYA-mediated Dt1 expression under LD likely preserves the vegetative activity of the SAM to produce more nodes in the e1-as/e3/E4 group. The designations e1, e3, and e4 refer to all dysfunctional alleles at these loci. Solid and dotted arrows indicate activation and lack of activation, respectively.