Root developmental plasticity enables plants to adapt to limiting or fluctuating nutrient conditions in the soil. When grown under nitrogen (N) deficiency, plants develop a more exploratory root system by increasing primary and lateral root length. However, mechanisms underlying this so-called foraging response remain poorly understood. We performed a genome-wide association study in Arabidopsis (Arabidopsis thaliana) and we show here that noncoding variations of the brassinosteroid (BR) biosynthesis gene DWARF1 (DWF1) lead to variation of the DWF1 transcript level that contributes to natural variation of root elongation under low N. In addition to DWF1, other central BR biosynthesis genes upregulated under low N include CONSTITUTIVE PHOTOMORPHOGENIC DWARF, DWF4, and BRASSINOSTEROID-6-OXIDASE2. Phenotypic characterization of knockout and knockdown mutants of these genes showed significant reduction of their root elongation response to low N, suggesting a systemic stimulation of BR biosynthesis to promote root elongation. Moreover, we show that low N-induced root elongation is associated with aboveground N content and that overexpression of DWF1 significantly improves plant growth and overall N accumulation. Our study reveals that mild N deficiency induces key genes in BR biosynthesis and that natural variation in BR synthesis contributes to the root foraging response, complementing the impact of enhanced BR signaling observed recently. Furthermore, these results suggest a considerable potential of BR biosynthesis to genetically engineer plants with improved N uptake.

根系发育可塑性使植物能够适应土壤中有限或波动的养分状况。在缺氮（N）的情况下生长时，植物会通过增加初级和侧根长度来开发更具探索性的根系。但是，对这种所谓的觅食反应的机制仍然知之甚少。我们在拟南芥（Arabidopsis thaliana）中进行了全基因组关联研究，我们在这里显示了油菜素甾体（BR）生物合成基因DWARF1（DWF1）的非编码变异导致DWF1转录水平的变异，这有助于根系在自然条件下根伸长的自然变异低N。除了DWF1在低N下上调的其他中央BR生物合成基因包括组成型光生性DWARF，DWF4和BRASSINOSTEROID-6-氧化酶2。这些基因的敲除和敲除突变体的表型特征表明，它们对低氮的根伸长响应显着降低，表明系统刺激BR生物合成以促进根伸长。此外，我们表明低N诱导的根伸长与地上N含量相关，并且DWF1的过度表达显着改善植物生长和整体氮素积累。我们的研究表明，轻度的氮缺乏会诱导BR生物合成中的关键基因，并且BR合成中的自然变异有助于根觅食反应，补充最近观察到的增强BR信号的影响。此外，这些结果表明，BR生物合成具有显着的潜力，可以通过基因工程改造具有更高氮吸收量的植物。