4.3 The function of LHY/CCA1 on flowering is distinct in LD and SD plants.
In Arabidopsis , LHY and CCA1 inhibit flowering under both LD and SD conditions (Mizoguchi et al., 2002; Wang & Tobin, 1998). The quadruple mutant of LHY/CCA1 -LIKE orthologsGmLCLa1 a2 b1 b2 lead to delayed flowering in soybean under LD conditions (Wang et al., 2019). While oslhy mutants exhibited late flowering in rice only under LD conditions, which similar as observed in soybean but different from that in Arabidopsis . The possible reason may be that the soybean and rice are both SD plants, yet the Arabidopsis is a LD plant. It allowed us to hypothesize that whether the LHY/CCA1 genes activate or inhibit flowering varies by species and is related to the photoperiod response of the species. Notably, it is not unique phenomenon. The function of PRRs and OsGI on controlling flowering are also associated with the photoperiod response in diverse species (Bendix, Marshall, & Harmon, 2015). In general, GI activates flowering in LD plants and suppresses flowering in SD plants (Bendix et al., 2015). While LHY/CCA1 may inhibits flowering in LD plants and activates flowering in SD plants.