Creative Research Initiatives, Division of Life Sciences, Korea University, Seoul 136-701, Korea.
Plant Cell Physiol. 2012 Oct;53(10):1802-14. doi: 10.1093/pcp/pcs123. Epub 2012 Sep 7.
Ubiquitin-dependent proteolysis regulates multiple aspects of plant growth and development, but little is known about its role in ambient temperature-responsive flowering. In addition to being regulated by daylength, the onset of flowering in many plants can also be delayed by low ambient temperatures. Here, we show that HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1 (HOS1), which encodes an E3 ubiquitin ligase, controls flowering time in response to ambient temperatures (16 and 23°C) and intermittent cold. hos1 mutants flowered early, and were insensitive to ambient temperature, but responded normally to vernalization and gibberellic acid. Genetic analyses suggested that this ambient temperature-insensitive flowering was independent of FLOWERING LOCUS C (FLC). Also, FLOWERING LOCUS T (FT) and TWIN SISTER OF FT (TSF) expression was up-regulated in hos1 mutants at both temperatures. The ft tsf mutation almost completely suppressed the early flowering of hos1 mutants at different temperatures, suggesting that FT and TSF are downstream of HOS1 in the ambient temperature response. A lesion in CONSTANS (CO) did not affect the ambient temperature-insensitive flowering phenotype of hos1-3 mutants. In silico analysis showed that FVE was spatiotemporally co-expressed with HOS1. A HOS1-green fluorescent protein (GFP) fusion co-localized with FVE-GFP in the nucleus at both 16 and 23°C. HOS1 physically interacted with FVE and FLK in yeast two-hybrid and co-immunoprecipitation assays. Moreover, hos1 mutants were insensitive to intermittent cold. Collectively, our results suggest that HOS1 acts as a common regulator in the signaling pathways that control flowering time in response to low ambient temperature.
泛素依赖性蛋白降解调节植物生长和发育的多个方面，但人们对其在环境温度响应开花中的作用知之甚少。除了受日照长度调控外，许多植物的开花时间也可以被低温延迟。在这里，我们发现 HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1（HOS1），它编码一个 E3 泛素连接酶，可响应环境温度（16 和 23°C）和间歇性寒冷来控制开花时间。hos1 突变体开花早，对环境温度不敏感，但对春化和赤霉素反应正常。遗传分析表明，这种对环境温度不敏感的开花与 FLOWERING LOCUS C（FLC）无关。此外，在 hos1 突变体中，FT 和 TSF 的表达在两种温度下均上调。在不同温度下，ft tsf 突变几乎完全抑制了 hos1 突变体的早期开花，表明 FT 和 TSF 是 HOS1 在环境温度响应中的下游基因。CONSTANS（CO）的突变不影响 hos1-3 突变体对环境温度不敏感的开花表型。计算机分析表明，FVE 与 HOS1 在时空上共表达。HOS1-绿色荧光蛋白（GFP）融合蛋白在 16°C 和 23°C 下均与 FVE-GFP 在核中共定位。HOS1 在酵母双杂交和共免疫沉淀实验中与 FVE 和 FLK 相互作用。此外，hos1 突变体对间歇性寒冷不敏感。综上所述，我们的结果表明，HOS1 作为一个共同的调节因子，在控制植物对低温响应开花时间的信号通路中发挥作用。
