Low nitrogen conditions accelerate flowering by modulating the phosphorylation state of FLOWERING BHLH 4 in Arabidopsis
Low nitrogen conditions accelerate flowering by modulating the phosphorylation state of FLOWERING BHLH 4 in Arabidopsis
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DOI：
10.1073/pnas.2022942118
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发表时间：
2021-05
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通讯作者：
Miho Sanagi;Shoki Aoyama;Akio Kubo;Yu Lu;Yasutake Sato;S. Ito;Mitsutomo Abe;Nobutaka Mitsuda;M. Ohme-Takagi;Takatoshi Kiba;Hirofumi Nakagami;F. Rolland;J. Yamaguchi;T. Imaizumi;Takeo Sato
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作者：
Miho Sanagi;Shoki Aoyama;Akio Kubo;Yu Lu;Yasutake Sato;S. Ito;Mitsutomo Abe;Nobutaka Mitsuda;M. Ohme-Takagi;Takatoshi Kiba;Hirofumi Nakagami;F. Rolland;J. Yamaguchi;T. Imaizumi;Takeo Sato
氮素有效性对植物生物量和作物产量有很大影响。氮的耗竭和过量施用都会影响作物产量和质量，并扰乱重要的生态系统。因此，了解氮调节影响生殖的发育转变（如开花）的机制对于可持续地提高作物产量至关重要。我们的研究确定FBH4是拟南芥氮响应开花的关键转录因子。氮水平控制FBH4磷酸化状态，其作为分子开关调节转录活性以诱导开花。细胞燃料传感器SnRK1催化FBH 4磷酸化并在高氮条件下负调节成花素水平。这些发现将使新的分子育种策略能够通过在不同氮条件下优化开花时间来实现更好的作物产量。氮（N）是一种重要的营养物质，影响植物的多个发育过程，包括开花。由于开花需要资源来发展生殖所需的库组织，因此养分的可用性与这一过程密切相关。低氮水平加速花的转变，然而，这种反应的分子机制还没有很好地理解。在这里，我们确定了FLOWARCHBHLH 4（FBH4）转录因子作为一个关键的调节器的N-响应开花拟南芥。低氮诱导的早花在fbh四重突变体中受到损害。我们发现，FBH4是一个高度磷酸化的蛋白质和FBH4磷酸化水平降低低N条件下。此外，减少的磷酸化促进FBH4核定位和直接靶CONSTANS（CO）和下游成花原FLOWERLOCUS T（FT）基因的转录激活。此外，我们证明了进化上保守的细胞燃料传感器SNF1相关激酶1（SnRK1），其激酶活性在低N条件下下调，直接磷酸化FBH4。SnRK1负调节CO和FT转录水平在高N条件下。总之，这些结果揭示了一种机制，N水平可以微调FBH4核定位通过调节磷酸化状态，以调节开花时间。除了在开花调控中的作用外，我们还发现FBH4参与了低氮诱导的营养再循环和再动员相关基因表达的上调。因此，我们的研究结果提供了深入了解N-响应生长阶段的转变和优化植物健身营养有限的条件下。
Significance Nitrogen availability has a large impact on plant biomass and crop production. Both depletion and excessive application of nitrogen affect crop yields and quality and disturb important ecosystems. Thus, understanding the mechanisms by which nitrogen regulates developmental transitions affecting reproduction, such as flowering, is important to sustainably improve crop yields. Our study identified FBH4 as a key transcription factor mediating nitrogen-responsive flowering in Arabidopsis. Nitrogen levels control the FBH4 phosphorylation state that modulates transcriptional activity as a molecular switch to induce flowering. The cellular fuel sensor SnRK1 catalyzes FBH4 phosphorylation and negatively regulates florigen levels in high nitrogen conditions. These findings will enable new molecular breeding strategies to achieve better crop yields through optimized flowering time under different nitrogen conditions. Nitrogen (N) is an essential nutrient that affects multiple plant developmental processes, including flowering. As flowering requires resources to develop sink tissues for reproduction, nutrient availability is tightly linked to this process. Low N levels accelerate floral transition; however, the molecular mechanisms underlying this response are not well understood. Here, we identify the FLOWERING BHLH 4 (FBH4) transcription factor as a key regulator of N-responsive flowering in Arabidopsis. Low N-induced early flowering is compromised in fbh quadruple mutants. We found that FBH4 is a highly phosphorylated protein and that FBH4 phosphorylation levels decrease under low N conditions. In addition, decreased phosphorylation promotes FBH4 nuclear localization and transcriptional activation of the direct target CONSTANS (CO) and downstream florigen FLOWERING LOCUS T (FT) genes. Moreover, we demonstrate that the evolutionarily conserved cellular fuel sensor SNF1-RELATED KINASE 1 (SnRK1), whose kinase activity is down-regulated under low N conditions, directly phosphorylates FBH4. SnRK1 negatively regulates CO and FT transcript levels under high N conditions. Together, these results reveal a mechanism by which N levels may fine-tune FBH4 nuclear localization by adjusting the phosphorylation state to modulate flowering time. In addition to its role in flowering regulation, we also showed that FBH4 was involved in low N-induced up-regulation of nutrient recycling and remobilization-related gene expression. Thus, our findings provide insight into N-responsive growth phase transitions and optimization of plant fitness under nutrient-limited conditions.