Abstract：
Legumes house nitrogen-fixing endosymbiotic rhizobia in specialised polyploid cells within root nodules. This results in a mutualistic relationship whereby the plant host receives fixed nitrogen from the bacteria in exchange for dicarboxylic acids. This plant-microbe interaction requires the regulation of multiple metabolic and physiological processes in both the host and symbiont in order to achieve highly efficient symbiosis. Recent studies have showed that the success of symbiosis is influenced by the circadian clock of the plant host. Medicago and soybean plants with altered clock mechanisms showed compromised nodulation and reduced plant growth. Furthermore, transcriptomic analyses revealed that multiple genes with key roles in recruitment of rhizobia to plant roots, infection and nodule development were under circadian control, suggesting that appropriate timing of expression of these genes may be important for nodulation. There is also evidence for rhythmic gene expression of key nitrogen fixation genes in the rhizobium symbiont, and temporal coordination between nitrogen fixation in the bacterial symbiont and nitrogen assimilation in the plant host may be important for successful symbiosis. Understanding of how circadian regulation impacts on nodule establishment and function will identify key plant-rhizobial connections and regulators that could be targeted to increase the efficiency of this relationship.
摘要：
豆科植物在根瘤内的特殊多倍体细胞中容纳固氮内共生根瘤菌。这导致相互关系,由此植物宿主从细菌接收固定的氮以交换二羧酸。这种植物-微生物相互作用需要调节宿主和共生体中的多种代谢和生理过程，以实现高效的共生。最近的研究表明，共生的成功受到植物宿主昼夜节律的影响。具有改变的时钟机制的紫花苜蓿和大豆植物显示出受影响的结瘤和降低的植物生长。此外，转录组学分析显示，在根瘤菌募集到植物根中具有关键作用的多个基因，感染和结节发育受到昼夜节律控制，提示这些基因表达的适当时机对于结瘤可能很重要。也有证据表明根瘤菌共生体中关键固氮基因的节律性基因表达，细菌共生体中的固氮与植物宿主中的氮同化之间的时间协调对于成功共生可能很重要。了解昼夜节律调节如何影响根瘤的建立和功能，将确定关键的植物-根瘤菌连接和调节因子，以提高这种关系的效率。
