Abstract
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.
Highlights
The transition from vegetative to reproductive stage is a critical event in the life cycle for seed-propagated plants
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) [1,2,3,4]
In our previous study, when E1 was overexpressed in soybean cultivar Kariyutaka, expression levels of GmFT2a and GmFT5a were decreased in the transgenic soybean compared with the wildtype [37]
Summary
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. 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) [1,2,3,4]. The FT protein, a phosphatidylethanolamine-binding (PEBP)related kinase, interacts with Flowering Locus D (FD), a bZIP protein, at the vegetative shoot apex. The FT–FD complex subsequently functions to specify flower meristem identity by activating floral meristem genes that start the flowering process, such as APETALA1, FRUITFUL and SEPALATA3 [5,6,7]
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