Background: Avocado is an important economic fruit tree that requires a lot of nitrogen (N) to support growth and development. Nitrate transporter (NRT) gene family plays an essential role in N uptake and use in plants. However, no systematic identification of the NRT gene family has been reported in avocado. Methods: Bioinformatic analysis was used to identify and characterize the NRT gene family in avocado. The five N additions (29.75, 59.50, 119.00, 178.50, and 238.00 mg/L N) were used to identify the N requirement of avocado seedlings based on physiological indexes, while RNA-seq was conducted to analyze the response of PaNRTs under low-N and high-N conditions. Results: Sixty-one members of the NRT gene family were identified and dispersed on 12 chromosomes in avocado. Many cis-regulatory elements (CREs) related to phytohormonal and stress response were found in the PaNRTs promoter regions. The avocado leaves in N3 have the highest activities of N-assimilating enzymes and N content as well as the lowest activities of antioxidant enzymes. Thus, 29.75 mg/L and 119.00 mg/L were chosen as low-N supply and normal-N supply for transcriptome analysis. The transcriptome analysis showed that PaNRT1.11, PaNRT1.22, PaNRT1.32, PaNRT1.33, PaNRT1.38, and PaNRT1.52 and PaNRT1.56 among PaNRT1 members were up-regulated under normal-N condition in the leaves or roots, suggesting that these genes might affect N absorption under nitrate-sufficient conditions in avocado. RT-qPCR analysis found the relative expression patterns of selected genes among four samples were consistent with transcriptome data, suggesting that transcriptome data were reliable. Conclusions: This study would provide valuable information for identifying the functions of the NRT gene family in avocado.
Keywords: PaNRTs; avocado; expression levels; nitrogen.