背景回顾：Nitrogen is critical for plant growth and development. With the increase of nitrogen fertilizer application, nitrogen use efficiency decreases, resulting in wasted resources. 

提出问题：In apple (Malus domestica) rootstocks, the potential molecular mechanism for improving nitrogen uptake efficiency to alleviate low nitrogen stress remains unclear. 

主要发现：We utilized multi-omics approaches to investigate the mechanism of nitrogen uptake in two apple rootstocks with different responses to nitrogen stress, Malus hupehensis and Malus sieversii. 

结果1-比较组学：Under low nitrogen stress, Malus sieversii showed higher efficiency in nitrogen uptake. Multi-omics analysis revealed substantial differences in the expression of genes involved in flavonoid and lignin synthesis pathway between the two materials, which were related to the corresponding metabolites. 

结果2-bHLH130-CHS：We discovered that basic helix-loop-helix 130 (bHLH130) transcription factor was highly negatively associated with the flavonoid biosynthetic pathway. bHLH130 may directly bind to the chalcone synthase gene (CHS) promoter and inhibit its expression. 

结果3-过表达验证：Overexpressing CHS increased flavonoid accumulation and nitrogen uptake. Inhibiting bHLH130 increased flavonoid biosynthesis while decreasing lignin accumulation, thus improving nitrogen uptake efficiency. 

结论：These findings revealed the molecular mechanism by which bHLH130 regulates flavonoid and lignin biosynthesis in apple rootstocks under low nitrogen stress.

Hypothesis model of role of bHLH130 in mediating apple rootstocks response to low nitrogen stress.

氮对植物的生长发育至关重要。随着氮肥用量的增加，氮肥利用效率会逐步降低，从而造成资源浪费。在苹果砧木中，提高氮吸收效率以缓解低氮胁迫的潜在分子机制仍不清楚。本文中，作者利用多组学方法研究了对低氮胁迫响应不同的两种苹果砧木，即湖北海棠和新疆野苹果的氮吸收机制。在低氮胁迫下，新疆野苹果对氮的吸收效率更高。多组学分析显示，两种材料中类黄酮和木质素合成途径相关基因的表达呈显著差异，这与相应的代谢产物有关。作者发现，bHLH130转录因子与类黄酮生物合成途径高度负相关。bHLH130可直接结合查尔酮合酶编码基因CHS的启动子并抑制其表达。CHS的过表达增加了类黄酮的积累和氮的吸收。抑制bHLH130增加了类黄酮的生物合成，同时减少了木质素的积累，从而提高了氮的吸收效率。这些发现揭示了bHLH130在低氮胁迫下调节苹果砧木中黄酮和木质素生物合成的分子机制。