Wang Zhen, Yang Ruiguang, Devisetty Upendra K, Maloof Julin N, Zuo Yang, Li Jingjing, Shen Yuxiao, Zhao Jian, Bao Manzhu, Ning Guogui
Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural UniversityWuhan, China.
BIO5 Institute, University of Arizona, TucsonAZ, USA.
Front Plant Sci. 2017 May 8;8:697. doi: 10.3389/fpls.2017.00697. eCollection 2017.
FLOWERING LOCUS T () and TERMINAL FLOWER1 () proteins share highly conserved amino acid residues but they play opposite regulatory roles in promoting and repressing the flowering response, respectively. Previous substitution models and functional analysis have identified several key amino acid residues which are critical for the promotion of flowering. However, the precise relationship between naturally occurring homologs and the mechanism of their role in flowering is still unclear. In this study, homologs from eight Rosaceae species, namely, and , were isolated. Three of these homologs were further characterized by functional analyses involving site-directed mutagenesis. The results showed that these homologs might have diverse functions despite sharing a high similarity of sequences or crystal structures. Functional analyses were conducted for the key FT amino acids, Tyr-85 and Gln-140. It revealed that homologs cannot promote flowering simply by substitution with key amino acid residues. Mutations of the IYN triplet motif within segment C of exon 4 can prevent the homolog from promoting the flowering. Furthermore, physical interaction of FT homologous or mutated proteins with the transcription factor FD, together with their lipid-binding properties analysis, showed that it was not sufficient to trigger flowering. Thus, our findings revealed that the divergence of flowering time modulating by homologs is independent to interaction and binding activities.
成花素（FLOWERING LOCUS T，FT）蛋白和终端花1（TERMINAL FLOWER1，TFL1）蛋白具有高度保守的氨基酸残基，但它们在促进和抑制开花反应中分别发挥相反的调控作用。先前的替代模型和功能分析已经确定了几个对促进开花至关重要的关键氨基酸残基。然而，天然存在的同源物之间的确切关系及其在开花中的作用机制仍不清楚。在本研究中，从八个蔷薇科物种中分离出了FT同源物，即苹果（Malus domestica）、梨（Pyrus bretschneideri）、草莓（Fragaria × ananassa）、桃（Prunus persica）、李（Prunus salicina）、樱桃（Prunus avium）、扁桃（Prunus dulcis）和悬钩子（Rubus idaeus）。通过定点诱变的功能分析对其中三个同源物进行了进一步表征。结果表明，尽管这些FT同源物具有高度相似的序列或晶体结构，但它们可能具有不同的功能。对关键的FT氨基酸Tyr-85和Gln-140进行了功能分析。结果表明，FT同源物不能简单地通过关键FT氨基酸残基的替代来促进开花。外显子4的C段内IYN三联体基序的突变可以阻止FT同源物促进开花。此外，FT同源或突变蛋白与转录因子FD的物理相互作用以及它们的脂质结合特性分析表明，这不足以触发开花。因此，我们的研究结果表明，FT同源物调节开花时间的差异与相互作用和结合活性无关。
