Key Laboratory of Soybean Molecular Design Breeding (2013DP173244), Northeast Institute of Geography and Agroecology, The Innovative Academy of Seed Design, Chinese Academy of Sciences, Harbin 150081, China.
College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
Plant Physiol. 2022 Jun 1;189(2):1021-1036. doi: 10.1093/plphys/kiac092.
Soybean (Glycine max) is highly sensitive to photoperiod, which affects flowering time and plant architecture and thus limits the distribution range of elite soybean cultivars. The major maturity gene E1 confers the most prominent effect on photoperiod sensitivity, but its downstream signaling pathway remains largely unknown. Here, we confirm that the encoded E1 protein is a transcriptional repressor. The expression of seven GmMDE genes (Glycine max MADS-box genes downregulated by E1) was suppressed when E1 was overexpressed and promoted when E1 was knocked out through clustered regularly-interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9)-mediated mutagenesis. These GmMDEs exhibited similar tissue specificity and expression patterns, including in response to photoperiod, E1 expression, and E1 genotype. E1 repressed GmMDE promoter activity. Results for two GmMDEs showed that E1 epigenetically silences their expression by directly binding to their promoters to increase H3K27me3 levels. The overexpression of GmMDE06 promoted flowering and post-flowering termination of stem growth. The late flowering phenotype of E1-overexpressing soybean lines was reversed by the overexpression of GmMDE06, placing GmMDE06 downstream of E1. The overexpression of GmMDE06 increased the expression of the soybean FLOWERING LOCUS T orthologs GmFT2a and GmFT5a, leading to feedback upregulation of GmMDE, indicating that GmMDE and GmFT2a/GmFT5a form a positive regulatory feedback loop promoting flowering. GmMDE06 also promoted post-flowering termination of stem growth by repressing the expression of the shoot identity gene Dt1. The E1-GmMDEs-GmFT2a/5a-Dt1 signaling pathway illustrates how soybean responds to photoperiod by modulating flowering time and post-flowering stem termination.
大豆对光周期非常敏感，这影响开花时间和植物结构，从而限制了优良大豆品种的分布范围。主要成熟基因 E1 对光周期敏感性的影响最为显著，但它的下游信号通路在很大程度上仍是未知的。在这里，我们证实编码的 E1 蛋白是一种转录阻遏物。当 E1 过表达时，七个 GmMDE 基因（受 E1 下调的 Glycine max MADS-box 基因）的表达受到抑制，而当 E1 通过簇状规则间隔短回文重复（CRISPR）/CRISPR 相关蛋白 9（Cas9）介导的诱变而被敲除时，其表达得到促进。这些 GmMDE 具有相似的组织特异性和表达模式，包括对光周期、E1 表达和 E1 基因型的反应。E1 抑制 GmMDE 启动子活性。对两个 GmMDE 的研究结果表明，E1 通过直接结合其启动子来增加 H3K27me3 水平，从而使它们的表达发生表观遗传沉默。GmMDE06 的过表达促进了开花和开花后茎生长的终止。E1 过表达大豆品系的晚花表型被 GmMDE06 的过表达逆转，从而将 GmMDE06 置于 E1 的下游。GmMDE06 的过表达增加了大豆 FLOWERING LOCUS T 同源物 GmFT2a 和 GmFT5a 的表达，导致 GmMDE 的反馈上调，表明 GmMDE 和 GmFT2a/GmFT5a 形成了一个促进开花的正调控反馈环。GmMDE06 通过抑制分生组织身份基因 Dt1 的表达，也促进了开花后茎生长的终止。E1-GmMDEs-GmFT2a/5a-Dt1 信号通路说明了大豆如何通过调节开花时间和开花后茎的终止来响应光周期。
