The phosphatidylethanolamine-binding protein (PEBP) family plays an important role in plant growth and development, flowering, seed formation, and dormancy. In this study, we searched for candidate genes for FLOWERING LOCUS T (FT) orthologs in the indigo plant, Polygonum tinctorium, using a leaf RNA-seq database. We identified nine PEBP family sequences, including five FT-like genes (PtFT1―5) in P. tinctorium. In the expression analysis under two different conditions, a 12 h photoperiod as a short-day condition and a 24 h photoperiod as a long-day condition, PtFT2 and PtFT4 were significantly upregulated under short-day conditions than under long-day conditions. In the photoperiodic response under short-day conditions with monochromatic blue LED light, PtFT2, PtFT4 and PtFT5 significantly increased during the light period of the day, peaking toward the middle or end of the light period. In addition, PtFT2 expression significantly increased in a time-dependent manner in leaves grown under short-day blue LED light conditions, whereas PtFT4 and PtFT5 levels gradually decreased. These results suggest that blue light-induced expression of PtFT2 in leaves under floral-inductive conditions may be involved in promoting flower bud formation in P. tinctorium.
Nakai et al. (Wed,) studied this question.