Plants generally enhance their root growth in the form of greater biomass and/or root length to boost nutrient uptake in response to short-term low nitrogen (LN). However, the underlying mechanisms of short-term LN-mediated root growth remain largely elusive. Our genome-wide association study, haplotype analysis, and phenotyping of transgenic plants showed that the crucial nitrate signaling component NIN-LIKE PROTEIN3.2 (ZmNLP3.2), a positive regulator of root biomass, is associated with natural variations in root biomass of maize (Zea mays L.) seedlings under LN. The monocot-specific gene AUXIN/INDOLE-3-ACETIC ACID14 (ZmAux/IAA14) exhibited opposite expression patterns to ZmNLP3.2 in ZmNLP3.2 knockout and overexpression lines, suggesting that ZmNLP3.2 hampers ZmAux/IAA14 transcription. Importantly, ZmAux/IAA14 knockout seedlings showed a greater root dry weight (RDW), whereas ZmAux/IAA14 overexpression reduced RDW under LN compared with wild-type plants, indicating that ZmAux/IAA14 negatively regulates the RDW of LN-grown seedlings. Moreover, in vitro and vivo assays indicated that AUXIN RESPONSE FACTOR19 (ZmARF19) binds to and transcriptionally activates ZmAux/IAA14, which was weakened by the ZmNLP3.2–ZmARF19 interaction. The zmnlp3.2 ZmAux/IAA14-OE seedlings exhibited further reduced RDW compared to ZmAux/IAA14 overexpression lines when subjected to LN treatment, corroborating the ZmNLP3.2–ZmAux/IAA14 interaction. Thus, our study reveals a ZmNLP3.2–ZmARF19–ZmAux/IAA14 module regulating root biomass in response to nitrogen limitation in maize.

中文翻译：

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NIN-LIKE PROTEIN3.2 在低氮条件下抑制玉米幼苗中抑制因子 Aux/IAA14 的表达并提高根系生物量


植物通常以更大的生物量和/或根长的形式促进其根系生长，以促进养分吸收以应对短期低氮 （LN）。然而，短期 LN 介导的根生长的潜在机制在很大程度上仍然难以捉摸。我们对转基因植物的全基因组关联研究、单倍型分析和表型分析表明，关键的硝酸盐信号成分 NIN-LIKE PROTEIN3.2 （ZmNLP3.2） 是根生物量的正调节因子，与 LN 下玉米 （Zea mays L.） 幼苗根生物量的自然变化有关。单子叶植物特异性基因 AUXIN/INDOLE-3-ACETIC ACID14 （ZmAux/IAA14） 在 ZmNLP3.2 敲除和过表达系中表现出与 ZmNLP3.2 相反的表达模式，表明 ZmNLP3.2 阻碍了 ZmMLP3.2 的转录。重要的是，ZmAux/IAA14 敲除幼苗显示出更高的根干重 （RDW），而与野生型植物相比，ZmAux/IAA14 过表达降低了 LN 下 RDW，表明 ZmAux/IAA14 负调控 LN 生长幼苗的 RDW。此外，体外和体内试验表明，生长素反应FACTOR19 （ZmARF19） 结合并转录激活 Zmäuux/IAA14，后者被 ZmNLP3.2-ZmARF19 相互作用削弱。当接受 LN 处理时，与 ZmAux/IAA14 过表达系相比，zmnlp3.2 ZmAux/IAA14-OE 幼苗表现出进一步降低的 RDW，证实了 ZmNLP3.2-ZmAux/IAA14 相互作用。因此，我们的研究揭示了 ZmNLP3.2–ZmARF19–ZmAux/IAA14 模块响应玉米氮的限制调节根系生物量。