Turned on by heat: differential expression of FT and LFY-like genes in Narcissus tazetta during floral transition

Abstract

In Narcissus tazetta, a monocotyledonous bulbous geophyte, floral initiation and differentiation occur within the bulb during the quiescent period in summer, when ambient temperatures are relatively high and the bulb is located underground with no foliage or roots. In many plant species, FLOWERING LOCUS T (FT) and its homologues are considered powerful promoters of flowering. The Narcissus FT gene homologue (NtFT) was isolated, and organ-specific expression patterns of NtFT during the annual cycle and reproductive development under different temperature regimes were analysed using quantitative reverse transcription–PCR (qRT–PCR) and RNA in situ hybridization. During floral induction, NtFT was not expressed in bulb scales, roots, or foliage leaves, but it was detected inside the bulb in the apical meristem and leaf primordia. The expression of another key flowering gene, NLF, the LEAFY homologue in N. tazetta, was also observed only in meristem and leaf primordia within the bulbs; however, its expression did not coincide with that of NtFT during meristem transition to reproductive stage. Under high temperatures (25–30 °C) in the dark, NtFT expression occurred simultaneously with floral induction timing, indicating that floral induction is affected by high temperatures but not by photoperiod or vernalization. Monitoring the apical meristem of Narcissus in February–August of two growing seasons under ambient and controlled storage conditions showed that transition to flowering is temperature dependent and varies between years. Lack of NtFT and NLF expression in foliage leaves suggests that flower initiation control in Narcissus differs from that in common model plants.

Conserved function of FLOWERING LOCUS T (FT) homologues as signals for storage organ differentiation

“…However, AcFT2 complements the late flowering of the Arabidopsis ft-1 mutant when expressed under control of the constitutive 35S promoter but not the SUC2 promoter, which is indicative of a limited mobility of this protein. Actually, a similar direct activation of the FT homologue, NtFT, at the apical meristem and leaf primordia inside the bulb was also reported for Narcissus [17], suggesting that floral initiation control in bulbs does not require a mobile signal.…”

Phylogenomic Analysis of the PEBP Gene Family from Kalanchoë

“…The FT protein is a key integrator among different flowering pathways in angiosperms that promotes flowering [73]. In many plant species FT homologs regulate aspects of plant development in response to photoperiod and temperature [48,51,62,74,75]. Thus, the extended family of FT genes identified in Kalanchoë might be of significant relevance to flower induction in the response to different environmental cues.…”

Crosstalk in the darkness: bulb vernalization activates meristem transition via circadian rhythm and photoperiodic pathway

“…In addition to the important and conserved role of FT as the 'florigen', other genes of this family serve in many plant species as "master" regulators of an array of functions. In geophytes, they are also involved in bulbing/ tuberization [1,45] and are associated with vernalization, photoperiod, and heat response [47,65]. In garlic, six FT homologs were identified [37], including AsFT2, a homolog of onion 'florigen', whose expression well correlates with flowering initiation in garlic [45,76].…”