Figure 8. An overview of the working model for the photoperiodic
flowering time pathway in soybean.
Parallel representations of the network under long-day conditions and
short-day conditions are shown as well as the genes that when mutated
infer photoperiod-insensitive flowering. Under long day conditions,
Phytochrome A homologs GmPHYA3 and GmPHYA2 promoteE1 expression and inhibit GmELF3 expression. E1up-regulates GmFT4a (a change-of-function FT that
suppresses flowering) and down-regulates GmFT2a andGmFT5a , all of which are FT homologs
(Nan et al., 2014;
Samanfar et al., 2017; Xia et al., 2012; Zhai et al., 2014).GmGIa is a GI homolog which inhibits GmFT2a (but
interestingly not GmFT5a ) thus delaying flowering under long-day
conditions (Watanabe
et al., 2011).
Under short day conditions, GmELF3 is expressed. GmELF3 repressesE1 by physically associating with the E1 promoter. This
leads to the release of the E1 suppression of the GmFTgenes, thus promoting flowering under short days
(Lu et al., 2017; Xia
et al., 2012). Natural variation in the GmFT gene family is at
least partially responsible for flowering time variation in soybean,
with several polymorphic sites significantly associated with flowering
time variation (Jiang
et al., 2019). Soybean plants which carry loss-of-function alleles forE1 , GmGIa , GmPHYA3 and GmPHYA2 exhibit
photoperiod insensitive flowering as higher transcript levels of theFT genes are present
(Xu et al., 2013).
Thus, these genes may represent strong candidates for elucidating
photoperiod-insensitivity in Cannabis .