NO FLOWERING IN SHORT DAY (NFL) is a bHLH transcription factor that promotes flowering specifically under short-day in Arabidopsis

Abstract

Flowering in plants is a dynamic and synchronized process where various cues including age, day length, temperature and endogenous hormones fine-tune the timing of flowering for reproductive success. Arabidopsis thaliana is a facultative long day (LD) plant where LD photoperiod promotes flowering. Arabidopsis still flowers under shortday (SD) conditions, albeit much later than in LD conditions. Although factors regulating the inductive LD pathway have been extensively investigated, the non-inductive SD pathway is much less understood. Here, we identified a key basic helix-loop-helix transcription factor called NFL (NO FLOWERING IN SHORT DAY) that is essential to induce flowering specifically under SD conditions in Arabidopsis. nfl mutants do not flower under SD conditions, but flower similar to the wild type under LD conditions. The no-flowering phenotype in SD is rescued either by exogenous application of gibberellin (GA) or by introducing della quadruple mutants in the nfl background, suggesting that NFL acts upstream of GA to promote flowering. NFL is expressed at the meristematic regions and NFL is localized to the nucleus. Quantitative RT-PCR assays using apical tissues showed that GA biosynthetic genes are downregulated and the GA catabolic and receptor genes are upregulated in the nfl mutant compared with the wild type, consistent with the perturbation of the endogenous GA biosynthetic and catabolic intermediates in the mutant. Taken together, these data suggest that NFL is a key transcription factor necessary for promotion of flowering under non-inductive SD conditions through the GA signaling pathway.

bHLH093/NFL and bHLH061 are required for apical meristem function in Arabidopsis thaliana

“…Based on analyses of fluorescence patterns obtained by expressing bHLHL093:YFP or GFP:bHLH093 under control of the cauliflower mosaic virus 35S promoter, we and others demonstrated that bHLH093 localizes to nuclei (Supplemental Fig. 4), 6 which is in accordance with the subcellular localization reported for SCREAM/ICE1 and SCREAM 2. 3 During the first 28 d post-germination under long-day growth conditions (16 h day/8 h night), the growth and development of rosette leaves occurred normally in a bhlh093-1/bhlh061-1 loss-offunction mutant.…”

“…Defective bolting, as observed with the bhlh093-1/bhlh061-1 mutant, is consistent with the lack of stem growth reported for gibberellin biosynthetic mutants, 22 and it is thus possible that bHLH093 and bHLH061 serve functions in regulating gibberellin biosynthesis in the shoot apex. Sharma et al 6 reported that the gibberellin profile was affected significantly in the apex of bhlh093 mutant plants, which provides further support for the role of GA imbalances in producing the observed phenotype. However, insufficient GA supply in biosynthetic mutants results in leaves of dramatically reduced size 22 and not the increased biomass and substantial curling observed with the bhlh093-1/bhlh061-1 line.…”

“…Sharma et al 6 recently demonstrated that mutation of bHLH093 leads to delayed flowering under short day conditions, with a corresponding decrease in gibberellin (GA) levels within apical tissues. Additionally, the transition to flowering in bhlh093 mutants can be restored with exogenous GA application or upon crossing with a della quadruple mutant, indicating that bHLH093 likely functions upstream of GA signaling.…”

MdbHLH93, an apple activator regulating leaf senescence, is regulated by ABA and MdBT2 in antagonistic ways

“…A previous report has shown that Arabidopsis bHLH93 promotes plant flowering under short‐day conditions by regulating the expression of gibberellin biosynthesis and metabolism‐associated genes (Sharma et al ., ). Considering the fact that gibberellins are positive regulators of leaf senescence (Chen et al ., , ), it will be interesting to determine whether bHLH93 also plays a role in gibberellin‐induced leaf senescence.…”

Genome-wide Analysis In Response to N and C Identifies New Regulators for root AtNRT2 Transporters

“…To our knowledge, the role of bHLH093 in the roots and in response to light has never been characterised before. The only information concerns a role in flowering promotion under non-inductive short-day conditions through the gibberellin pathway (Sharma et al, 2016).…”