GmFT4, a Homolog of FLOWERING LOCUS T, Is Positively Regulated by E1 and Functions as a Flowering Repressor in Soybean
Is Positively Regulated by E1 and Functions as a Flowering
Repressor in Soybean. PLoS ONE 9(2): e89030. doi:10.1371/journal.pone.0089030
GmFT4, a Homolog of FLOWERING LOCUS T , Is Positively Regulated by E1 and Functions as a Flowering Repressor in Soybean
Hong Zhai 0
Shixiang Lu 0
Shuang Liang 0
Hongyan Wu 0
Xingzheng Zhang 0
Baohui Liu 0
Fanjiang Kong 0
Xiaohui Yuan 0
Jing Li 0
Zhengjun Xia 0
David E. Somers, Ohio State University, United States of America
0 1 Key Laboratory of Soybean Molecular Design Breeding, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences , Harbin, Heilongjiang , China , 2 College of Life Science, Northeast Agricultural University , Harbin, Heilongjiang , China
The major maturity gene E1 has the most prominent effect on flowering time and photoperiod sensitivity of soybean, but the pathway mediated by E1 is largely unknown. Here, we found the expression of GmFT4, a homolog of Flowering Locus T, was strongly up-regulated in transgenic soybean overexpressing E1, whereas expression of flowering activators, GmFT2a and GmFT5a, was suppressed. GmFT4 expression was strongly up-regulated by long days exhibiting a diurnal rhythm, but down-regulated by short days. Notably, the basal expression level of GmFT4 was elevated when transferred to continous light, whereas repressed when transferred to continuous dark. GmFT4 was primarily expressed in fully expanded leaves. Transcript abundance of GmFT4 was significantly correlated with that of functional E1, as well as flowering time phenotype in different cultivars. Overexpression of GmFT4 delayed the flowering time in transgenic Arabidopsis. Taken together, we propose that GmFT4 acts downstream of E1 and functions as a flowering repressor, and the balance of two antagonistic factors (GmFT4 vs GmFT2a/5a) determines the flowering time of soybean.
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Funding: This work was supported by National Natural Science Foundation of China (31271742 and 31301338), Chinese Academy of Sciences (Hundred Talents
Program, KZCX2-EW-303, XDA08010105), and Natural Science Foundation of Heilongjiang Province of China (ZD201120). The funders had no role in study design,
data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
The transition from vegetative to reproductive stage is a critical
event in the life cycle for seed-propagated plants. Seasonal changes
in day length are perceived in leaves, while the responses occur at
the apex by long-distance signaling. Florigen, the molecule(s) that
migrates from leaves to apical meristem to initiate flowering was
proposed by Russian plant physiologist Mikhail Chailakhyan
(1937) based on grafting experiments. Recent advances made in
Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) have
demonstrated that FLOWERING LOCUS T (FT) protein
produced in leaves, is a florigen that moves through the phloem
to the shoot apical meristem (SAM) [14].
The FT protein, a phosphatidylethanolamine-binding
(PEBP)related kinase, interacts with Flowering Locus D (FD), a bZIP
protein, at the vegetative shoot apex. The FTFD complex
subsequently functions to specify flower meristem identity by
activating floral meristem genes that start the flowering process,
such as APETALA1, FRUITFUL and SEPALATA3 [57].
The expression of FT is principally regulated by the CONSTANS
(CO) gene, a central regulator that accelerates flowering in the long
day pathway (for long day plants), which is modulated by the
circadian clock and day length [8]. The photoperiodic response in
Arabidopsis thaliana requires the precise regulation of CO and FT
expression coinciding with a photosensitive phase [910].
Apart from FT, two other PEBP family members, TWIN
SISTER OF FT (TSF) and TERMINAL FLOWER 1 (TFL1), are also
involved in the control of flowering. TSF is a flowering activator,
and TFL1 is a flowering repressor. TSF is the closest homolog of
FT in Arabidopsis and is thought to be an additional integrator of
flowering time pathways. The mRNA levels of TSF and FT
showed similar patterns of diurnal oscillation and response to
photoperiods [11]. Both FT and TSF are expressed in the vascular
tissue of plant leaves but are spatially different, with TSF expressed
mainly in hypocotyls while FT expressed in cotyledons and leaves
[11,12]. TFL1, a shoot meristem identity gene, is expressed
specifically in the shoot apical meristem (SAM) and represses the
transition to flowering [1316].
FT acting as a floral activator is widely conserved in plant
species, although FT mRNA can be regulated by distinct
mechanisms among different species even within long-day (LD)
or short-day (SD) plant species [17]. Overexpression of FT
orthologs, Hd3a and RFT1, generally showed an early-flowering
phenotype, while mutations in FT led to a late flowering
phenotype in rice [1820]. Similarly, many functional FT
orthologs were characterized, e.g. GmFT2a a (...truncated)