Transcriptomic Sequencing and Co-Expression Network Analysis on Key Genes and Pathways Regulating Nitrogen Use Efficiency in Myriophyllum aquaticum

Massively input and accumulated ammonium is one of the main causes of eutrophication in aquatic ecosystems, which severely deteriorates water quality. Previous studies showed that one of the commonly used macrophytes, Myriophyllum aquaticum, was capable of not only withstanding ammonium of high concentration, but also efficiently assimilating extracellular ammonium to constitutive amino acids and proteins. However, the genetic mechanism regulating such efficient nitrogen metabolism in M. aquaticum is still poorly understood. Therefore, RNA-based analysis was performed in this study to understand the ammonium regulatory mechanism in M. aquaticum in response to various concentrations of ammonium. A total of 7721 genes were differentially expressed, of which those related to nitrogen-transport, assimilation, and remobilization were highly-regulated in response to various concentrations of ammonium. We have also identified transcription factors and protein kinases that were rapidly induced in response to ammonium, which suggests their involvement in ammonium-mediated signalling. Meanwhile, secondary metabolism including phenolics and anthocyanins biosynthesis was also activated in response to various concentrations of ammonium, especially at high ammonium concentrations. These results proposed a complex physiological and genetic regulation network related to nitrogen, carbohydrate, transcription factors, and secondary metabolism for nitrogen use efficiency in M. aquaticum.