Cao Jingjing, Zhou Yu, Tian Tao, Ji Jie, Deng Yan, Guan Yuhao, Qi Yongmei, Wang Longxiang, Wang Longlong, Huang Yibo, Fan Qiuling, Duanmu Deqiang
State Key Laboratory of Agricultural Microbiology, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, 430070, China.
School of Biological and Food Engineering, Engineering Research Center for Development and High Value Utilization of Genuine Medicinal Materials in North Anhui Province, Suzhou University, Suzhou, Anhui, 234000, China.
BMC Biol. 2024 Dec 18;22(1):293. doi: 10.1186/s12915-024-02088-5.
The mutualistic beneficial relationship between legume plants and rhizobia enables the growth of plants in nitrogen-limiting conditions. Rhizobia infect legumes through root hairs and trigger nodule organogenesis in the cortex. The plant hormone cytokinin plays a pivotal role in regulating both rhizobial infection and the initiation of nodule development. However, the mechanism used by the cytokinin output module to control symbiosis remains poorly documented.
In this study, we identified a cytokinin signaling output component encoded by the Type-B RESPONSE REGULATOR (RRB) gene, LjRRB12, which is expressed in Lotus japonicus nodule primordia and young nodules. Disruption of LjRRB12 leads to a reduction in nodulation and to an increase in the number of infection threads. Overexpression of LjRRB12, an active form of the LjRRB12 protein, induces nodule-like structures in wild type and hit1 (hyperinfected 1/lotus histidine kinase 1) mutants but not in nin2 (nodule inception 2) mutants. Additionally, we utilized nCUT&Tag and EMSA to demonstrate that LjRRB12 can bind a CE (cytokinin response element) from the LjNIN promoter.
Our results provide a deeper understanding of nodule organogenesis by establishing a link between the cytokinin signal and the transcriptional regulation of LjNIN.
豆科植物与根瘤菌之间的互利共生关系使植物能够在氮限制条件下生长。根瘤菌通过根毛感染豆科植物，并在皮层中触发根瘤器官发生。植物激素细胞分裂素在调节根瘤菌感染和根瘤发育起始过程中起关键作用。然而，细胞分裂素输出模块控制共生的机制仍知之甚少。
在本研究中，我们鉴定出一个由B型响应调节因子（RRB）基因LjRRB12编码的细胞分裂素信号输出成分，该基因在百脉根根瘤原基和幼根瘤中表达。LjRRB12的破坏导致根瘤形成减少，感染线数量增加。LjRRB12蛋白的活性形式LjRRB12的过表达在野生型和hit1（超感染1/百脉根组氨酸激酶1）突变体中诱导形成类根瘤结构，但在nin2（根瘤起始2）突变体中未诱导形成。此外，我们利用nCUT&Tag和EMSA证明LjRRB12可以结合LjNIN启动子的一个细胞分裂素响应元件（CE）。
我们的结果通过建立细胞分裂素信号与LjNIN转录调控之间的联系，为根瘤器官发生提供了更深入的理解。
