提出问题：Both lateral roots and nodules form on the root system and the developmental coordination of these organs according to reduced nitrogen (N) availability remains elusive.

主要发现：We show that the Compact Root Architecture 2 (MtCRA2) receptor-like kinase is essential to promote the initiation of early symbiotic nodulation and to inhibit root growth in response to low-N.

生长素合成：MtCEP1 peptides can activate MtCRA2 under N-starvation conditions, leading to a repression of MtYUC2auxin biosynthesis gene expression, and therefore of auxin root responses. Accordingly, the compact root architecture phenotype of cra2 can be mimicked by an auxin treatment or by over-expressing MtYUC2, and conversely, a treatment with YUC inhibitors or a MtYUC2 knock-out rescues the cra2 root phenotype.

乙烯信号：The MtCEP1-activated CRA2 can additionally interact with and phosphorylate the MtEIN2 ethylene signaling component at Ser⁶⁴³ and Ser⁹²⁴, preventing its cleavage and therefore repressing ethylene responses, thus locally promoting the root susceptibility to rhizobia. In agreement, the cra2 low nodulation phenotype is rescued by an ein2 mutation.

结论：Overall, by reducing auxin biosynthesis and inhibiting ethylene signaling, the MtCEP1/MtCRA2 pathway balances root and nodule development under low-N conditions.

p.s. 乙烯信号组分EIN2正常定位于胞质的内质网膜上，在存在乙烯时，其C端被剪切入核，激活下游的乙烯信号。

 通讯作者