Abstract
We show that the key flowering regulators encoded by Phalaenopsis aphrodite FLOWERING LOCUS T1 (PaFT1) and PaFD share high sequence homologies to these from long-day flowering Arabidopsis and short-day flowering rice. Interestingly, PaFT1 is specifically up-regulated during flowering inductive cooling treatment but is not subjected to control by photoperiod in P. aphrodite. Phloem or shoot apex-specific expression of PaFT1 restores the late flowering of Arabidopsis ft mutants. Moreover, PaFT1 can suppress the delayed flowering caused by SHORT VEGATATIVE PHASE (SVP) overexpression as well as an active FRIGIDA (FRI) allele, indicating the functional conservation of flowering regulatory circuit in different plant species. PaFT1 promoter:GUS in Arabidopsis showed similar staining pattern to that of Arabidopsis FT in the leaves and guard cells but different in the shoot apex. A genomic clone or heat shock-inducible expression of PaFT1 is sufficient to the partial complementation of the ft mutants. Remarkably, ectopic PaFT1 expression also triggers precocious heading in rice. To further demonstrate the functional conservation of the flowering regulators, we show that PaFD, a bZIP transcription factor involved in flowering promotion, interacts with PaFT1, and PaFD partially complemented Arabidopsis fd mutants. Transgenic rice expressing PaFD also flowered early with increased expression of rice homologues of APETALA1 (AP1). Consistently, PaFT1 knock-down Phalaenopsis plants generated by virus-induced gene silencing exhibit delayed spiking. These studies suggest functional conservation of FT and FD genes, which may have evolved and integrated into distinct regulatory circuits in monopodial orchids, Arabidopsis and rice that promote flowering under their own inductive conditions.
Highlights
Plants have evolved mechanisms to integrate environmental and developmental signals and precisely control the transition terminating vegetative growth and initiating the formation of flowers.PLOS ONE | DOI:10.1371/journal.pone.0134987 August 28, 2015Functional studies of Phalaenopsis FT and FD genesIn Arabidopsis, flowering is triggered by multiple pathways [1] converging on a few integrators such as FLOWERING LOCUS T (FT) [2]
We show that the key flowering regulators encoded by Phalaenopsis aphrodite FLOWERING LOCUS T1 (PaFT1) and PaFD share high sequence homologies to these from long-day flowering Arabidopsis and short-day flowering rice
To further demonstrate the functional conservation of the flowering regulators, we show that PaFD, a bZIP transcription factor involved in flowering promotion, interacts with PaFT1, and PaFD partially complemented Arabidopsis fd mutants
Summary
Plants have evolved mechanisms to integrate environmental and developmental signals and precisely control the transition terminating vegetative growth and initiating the formation of flowers.PLOS ONE | DOI:10.1371/journal.pone.0134987 August 28, 2015Functional studies of Phalaenopsis FT and FD genesIn Arabidopsis, flowering is triggered by multiple pathways [1] converging on a few integrators such as FLOWERING LOCUS T (FT) [2]. FT-like genes are well conserved among flowering plants and were reported to play a role of flowering activators in plants other than Arabidopsis, including tomato [7], squash [8] and rice [9,10]. One example target of the FT-FD complex is APETALA1 (AP1), a meristem identity gene; another target is SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), which promotes the expression of another meristem identity gene called LEAFY (LFY). Both AP1 and LFY expression are repressed during vegetative growth, and this repression is released upon arrival of FT in the meristem [12]
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