Improvement of in vitro bulblet formation in garlic under continuous-light condition is tightly associated with FLOWERING LOCUS T-like gene expression

Garlic (Allium sativum L.) in vitro bulblet formation is elicited by low temperatures and subsequent long photoperiods. FLOWERING LOCUS T (FT)-like genes control photoperiod-dependent storage organ formation, such as bulbing in onion (Allium cepa L.); however, the involvements of FT-like genes for in vitro bulblet formation in garlic are not enough understood. Here, we examined the effects of cold treatment durations and subsequent photoperiods under short-day (SD; 8 h light), long-day (LD; 16 h light), and continuous-light (CL; 24 h light) conditions on in vitro bulblet formation and temporal expression of FT-like genes in garlic. In vitro bulblet formation was substantially promoted under CL, compared with LD and SD conditions after 90 days of cold treatment. Six FT-like genes (AsFT1-AsFT6) identified in this study were associated with specific amino acid residues or motifs in floral signal molecule florigen. AsFT1 expression was markedly increased under CL after cold treatment and was considerably higher than under LD and SD conditions. Therefore, the promotion of in vitro bulblet formation induced by CL was strongly associated with AsFT1 expression. Moreover, AsFT3 expression appeared to be associated with in vitro bulblet formation induced by LD and CL. Taken together, our results suggest CL condition accelerates in vitro bulblet formation after shorter durations of cold treatment and affects the inductions of AsFT-like genes. These findings will help improve tissue culture methods to achieve disease-free seeds production and further our understanding of bulbing mechanisms in garlic. Key messageContinuous-light condition markedly promotes in vitro bulblet formation and characteristic expression of AsFT1 gene in garlic.