Abstract
Asiatic hybrid lily leaves emerge from their bulbs in spring, after cold exposure in winter, and the plant then blooms in early summer. We identified four FLOWERING LOCUS T (FT)-like genes, LhFT1, LhFT4, LhFT6, and LhFT8, from an Asiatic hybrid lily. Floral bud differentiation initiated within bulbs before the emergence of leaves. LhFT genes were mainly expressed in bulb scales, and hardly in leaves, in which the FT-like genes of many plants are expressed in response to environmental signals. LhFT1 was expressed in bulb scales after vernalization and was correlated to flower bud initiation in two cultivars with different flowering behaviors. LhFT8 was upregulated in bulb scales after cold exposure and three alternative splicing variants with a nonsense codon were simultaneously expressed. LhFT6 was upregulated in bulb scales after flower initiation, whereas LhFT4 was expressed constantly in all organs. LhFT1 overexpression complemented the late-flowering phenotype of Arabidopsis ft-10, whereas that of LhFT8 did so partly. LhFT4 and LhFT6 overexpression could not complement. Yeast two-hybrid and in vitro analyses showed that the LhFT1 protein interacted with the LhFD protein. LhFT6 and LhFT8 proteins also interacted with LhFD, as observed in AlphaScreen assay. Based on these results, we revealed that LhFT1 acts as a floral activator during floral bud initiation in Asiatic hybrid lilies. However, the biological functions of LhFT4, LhFT6, and LhFT8 remain unclear.
Highlights
The genus Lilium consists of approximately 100 species that are distributed throughout the cold and temperate regions of the Northern Hemisphere and are classified into seven sections (van Tuyl et al, 2018)
Before the investigation of the temporal and spatial expression of LhFT genes in pre-vernalization and during planting, we examined the floral development stages of the shoot apical meristem (SAM) of bulbs in each phase (Figure 1I)
Aspartic acid (D) at position 17 and valine (V) at position 18, which are important for the transport of FLOWERING LOCUS T (FT), are conserved in the LhFT1, LhFT6, and LhFT8 proteins. These results suggest that LhFT1 and LhFT8 are very similar to FT-like proteins, whereas LhFT4 is similar to TERMINAL FLOWER 1 (TFL1)-like proteins
Summary
The genus Lilium consists of approximately 100 species that are distributed throughout the cold and temperate regions of the Northern Hemisphere and are classified into seven sections (van Tuyl et al, 2018). Asiatic hybrid lilies are derived from interspecific hybridization among L. dauricum, L. maculatum, L. lacifolium, etc., which are species that belong to the sections Sinomartagon and Daurolirion (MarasekCiolakowska et al, 2018). These plants are characterized by an upward-facing flower and Expression of FT-Like Genes in Bulb Scales little or no fragrance (Dole and Wilkins, 2005). The color of their flowers is often uniform or with a contrasting perianth segment tips and/or throat, and they exhibit a wide variety of flower colors in different shades, from white to red and yellow (Yamagishi, 2013). Commercial Asiatic hybrid lily cultivars are usually propagated by bulbs, rather than seeds (Beattie and White, 1993)
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