Orphan genes (OGs) are unique to the specific species or lineage, and whose homologous sequences cannot be found in other species or lineages. Furthermore, these genes lack recognizable domains or functional motifs, which make their characterization difficult. Here, we identified a Brassica rapa OG named BOLTING RESISTANCE 2 (BR2) that could positively modulate bolting resistance. The expression of BR2 was developmentally regulated and the BR2 protein was localized to the cell membrane. BR2 overexpression not only markedly delayed flowering time in Arabidopsis transgenic plants, but substantially affected the development of leaves and flower organs. Flowering repressor AtFLC gene was significantly up-regulated transcribed in Arabidopsis BR2 overexpression lines, while AtFT and AtSOC1 expression was decreased. In addition, the BR2 expression was enhanced in bolting-resistant type Chinese cabbage and was reduced in non-resistant type. Moreover, chilling stress inhibited the BR2 expression levels. Overexpression of BR2 also delayed flowering time in Chinese cabbage. In vernalized Chinese cabbage BR2 overexpression plants, BrVIN3.b and BrFRI were significantly down-regulated, while BrFLC5 was substantially up-regulated. Key floral factors, including three BrSOC1s, two BrLFYs, and four BrFTs were down-regulated. The expression changes of these key genes were consistent with the delayed flowering phenotype of Chinese cabbage BR2 overexpressing plants. Thus, we predicted that BR2 may predominantly function via the vernalization pathway. Our findings propose that the OG BR2 acts as a novel modulator of flowering time in Chinese cabbage, which provides a new insight on the breeding of varieties that are resistant to bolting.

中文翻译：

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孤儿基因 BR2 通过春化途径正向调控大白菜抽薹抗性


孤儿基因 （OG） 是特定物种或谱系所特有的，其同源序列在其他物种或谱系中找不到。此外，这些基因缺乏可识别的结构域或功能基序，这使得它们的表征变得困难。在这里，我们确定了一种名为 BOLTING RESISTANCE 2 （BR2） 的 Brassica rapa OG，它可以正向调节螺栓阻力。BR2 的表达受发育调节，BR2 蛋白定位于细胞膜。BR2 过表达不仅显著延迟了拟南芥转基因植株的开花时间，而且显著影响了叶片和花器官的发育。在拟南芥 BR2 过表达系中，开花阻遏物 AtFLC 基因的转录显著上调，而 AtFT 和 AtSOC1 的表达降低。此外，BR2 在抗抽薹型大白菜中表达增强，在非抗性型中表达降低。此外，寒冷应激抑制了 BR2 表达水平。BR2 的过表达也延迟了大白菜的开花时间。在春化大白菜 BR2 过表达植物中，BrVIN3.b 和 BrFRI 显著下调，而 BrFLC5 显著上调。关键花因子 （包括 3 个 BrSOC1 、 2 个 BrLFYs 和 4 个 BrFT ） 被下调。这些关键基因的表达变化与大白菜 BR2 过表达植株的延迟开花表型一致。因此，我们预测 BR2 可能主要通过春化途径发挥作用。我们的研究结果表明，OG BR2 是大白菜开花时间的新型调节剂，这为抗抽薹品种的培育提供了新的见解。