Proteins from the FLOWERING LOCUS T‐like subclade of the PEBP family act antagonistically to regulate floral initiation in tobacco

Abstract

SUMMARYFlowering is an important agronomic trait that often depends on the integration of photoperiod, vernalization, gibberellin and/or autonomous signaling pathways by regulatory proteins such as FLOWERING LOCUS T (FT), a member of the phosphatidylethanolamine-binding protein (PEBP) family. Six PEBP family proteins control flowering in the model plant Arabidopsis thaliana, and their regulatory functions are well established, but variation in the number and structural diversity of PEBPs in different species means their precise functions must be determined on a case-by-case basis. We isolated four novel FT-like genes from Nicotiana tabacum (tobacco), and determined their expression profiles in wild-type plants and their overexpression phenotypes in transgenic plants. We found that all four genes were expressed in leaves under short-day conditions, and at least NtFT3 expression was restricted to phloem companion cells. We also found that the NtFT1, NtFT2 and NtFT3 proteins are floral inhibitors (atypical for FT-like proteins), whereas only NtFT4 is a floral inducer. We were unable to detect the expression of these genes under long-day conditions, suggesting that all four tobacco FT-like proteins may control flowering in response to short days. Phylogenetic analysis of PEBP family proteins and their functions in different solanaceous species confirmed that gene duplication and divergence within the FT-like clade has led to the evolution of antagonistic regulators that may help to fine-tune floral initiation in response to environmental cues.

A Virus-Induced Assay for Functional Dissection and Analysis of Monocot and Dicot Flowering Time Genes

“…1A). Consistent with the fact that NtFT4 is known to be the true AtFT ortholog in day-neutral tobacco (Harig et al, 2012), viral expression of NtFT4 from PVX/NtFT4 in MM plants was able to induce flowering under noninductive LD ( Fig. 1B; Supplemental Fig.…”

“…We then used this VIF in three different approaches to evaluate the influence of individual amino acids on AtFT activity, the impact of polypeptide tags on AtFT function, and the roles of monocot and dicot FT genes in flowering. To investigate the mechanism through which VIF works, we analyzed the temporal expression profiles of the four known day-neutral tobacco FT-like genes NtFT1, NtFT2, NtFT3, and NtFT4 (Harig et al, 2012) in MM plants grown in SD (Fig. 1).…”

“…In Arabidopsis (Arabidopsis thaliana), the major component of florigen is a protein encoded by Flowering Locus T (AtFT; Koornneef et al, 1991;Kardailsky et al, 1999;Kobayashi et al, 1999;Turck et al, 2008;Pin and Nilsson, 2012). Many AtFT orthologs have been isolated from other species, for instance, rice (Oryza sativa) Hd3a, tomato SFT, tobacco (Nicotiana tabacum) NtFT4, and sugar beet (Beta vulgaris) BvFT2, and transgenic overexpression of these genes results in early flowering (Kojima et al, 2002;Lifschitz et al, 2006;Pin et al, 2010;Harig et al, 2012). Instead of generating transgenic plants, virus-based technique has also been used as a more rapid method to demonstrate the florigenic activity of FT proteins and RNA.…”

Molecular characterization and functional analysis of a Flowering locus T homolog gene from a Phalaenopsis orchid

“…Similar to the FT genes from other plant species, the PhFT contained 3 introns and 4 exons (Figure 2). Although the sizes of FT introns vary across different plant species, the lengths of the second (62 bp) and third (41 bp) exons seem to be conserved across different plant species (Fukuda et al, 2011;Harig et al, 2012). PhFT had a highly conserved amino acid sequence from the N-terminal to C-terminal, which was concomitant with the FT proteins of C. goeringii, Oncidium Gower Ramsey, G. hirsutum, P. pyrifolia, O. rufipogon, P. mume, and H. vulgare subsp vulgare (Figure 3).…”

“…In sugar beet Beta vulgaris, FT1 (BvFT1) represses flowering (Pin et al, 2010). In tobacco Nicotiana tabacum, FT1, FT2, and FT3 proteins act as floral inhibitors (Harig et al, 2012). Furthermore, FT regulates stomatal opening and modulates lateral shoot outgrowth in A. thaliana (Kinoshita et al, 2011;Hiraoka et al, 2013) and affects the architecture but not floral organogenesis in cotton (McGarry et al, 2013).…”