The nuclear pore complex profoundly affects the timing of flowering; however, the underlying mechanisms are poorly understood. Here, we report that Nucleoporin96 (Nup96) acts as a negative regulator of long-day photoperiodic flowering in Arabidopsis (Arabidopsis thaliana). Through multiple approaches, we identified the E3 ubiquitin ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE1 (HOS1) and demonstrated its interaction in vivo with Nup96. Nup96 and HOS1 mainly localize and interact on the nuclear membrane. Loss of function of Nup96 leads to destruction of HOS1 proteins without a change in their mRNA abundance, which results in overaccumulation of the key activator of long-day photoperiodic flowering, CONSTANS (CO) proteins, as previously reported in hos1 mutants. Unexpectedly, mutation of HOS1 strikingly diminishes Nup96 protein level, suggesting that Nup96 and HOS1 are mutually stabilized and thus form a novel repressive module that regulates CO protein turnover. Therefore, the nup96 and hos1 single and nup96 hos1 double mutants have highly similar early-flowering phenotypes and overlapping transcriptome changes. Together, this study reveals a repression mechanism in which the Nup96-HOS1 repressive module gates the level of CO proteins and thereby prevents precocious flowering in long-day conditions.

中文翻译：

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Nup96 和 HOS1 相互稳定并控制 CONSTANS 蛋白水平，赋予拟南芥长日照光周期开花调节作用。

核孔复合体深刻影响开花时间；然而，人们对其根本机制知之甚少。在此，我们报道核孔蛋白96（Nup96）在拟南芥（Arabidopsis thaliana）中充当长日照光周期开花的负调节剂。通过多种方法，我们鉴定了 E3 泛素连接酶高表达渗透响应基因 1 (HOS1)，并证明了其在体内与 Nup96 的相互作用。Nup96和HOS1主要定位在核膜上并相互作用。Nup96 功能丧失会导致 HOS1 蛋白被破坏，而其 mRNA 丰度没有变化，从而导致长日照光周期开花的关键激活剂 CONSTANS (CO) 蛋白过度积累，如之前在 hos1 突变体中报道的那样。出乎意料的是，HOS1 的突变显着降低了 Nup96 蛋白水平，表明 Nup96 和 HOS1 相互稳定，从而形成调节 CO 蛋白周转的新型抑制模块。因此，nup96和hos1单突变体和nup96 hos1双突变体具有高度相似的早花表型和重叠的转录组变化。总之，这项研究揭示了一种抑制机制，其中 Nup96-HOS1 抑制模块控制 CO 蛋白的水平，从而防止长日照条件下的早花。