Nitrogen Assimilation Related Genes in Brassica napus: Systematic Characterization and Expression Analysis Identified Hub Genes in Multiple Nutrient Stress Responses

Nitrogen (N) is an essential macronutrient for plants. However, little is known about the molecular regulation of N assimilation in Brassica napus, one of the most important oil crops worldwide. Here, we carried out a comprehensive genome-wide analysis of the N assimilation related genes (NAGs) in B. napus. A total of 67 NAGs were identified encoding major enzymes involved in N assimilation, including asparagine synthetase (AS), glutamate dehydrogenase (GDH), glutamine oxoglutarate aminotransferase (GOGAT), glutamine synthetase (GS), nitrite reductase (NiR), nitrate reductase (NR). The syntenic analysis revealed that segmental duplication and whole-genome duplication were the main expansion pattern during gene evolution. Each NAG family showed different degrees of differentiation in characterization, gene structure, conserved motifs and cis-elements. Furthermore, diverse responses of NAG to multiple nutrient stresses were observed. Among them, more NAGs were regulated by N deficiency and ammonium toxicity than by phosphorus and potassium deprivations. Moreover, 12 hub genes responding to N starvation were identified, which may play vital roles in N utilization. Taken together, our results provide a basis for further functional research of NAGs in rapeseed N assimilation and also put forward new points in their responses to contrasting nutrient stresses.