Molecular evolutionary analysis and expression patterns of nitrogen assimilation-related gene families in Lycium ruthenicum under salt stress

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Nitrogen assimilation plays a critical role in the response of plants to salt stress. In this study, bioinformatics and computational biology methods were employed to identify members of the Lycium GS, GOGAT, and GDH gene families, and analyzed their expression patterns and transcriptional regulatory networks under salt stress in black wolfberry (Lycium ruthenicum). In addition, the adaptive evolutionary mechanisms of the black wolfberry Fd-GOGAT gene were explored. The results showed that the genomes or transcriptomes of Lycium species contain two to four GS genes, two GOGAT genes, and three to four GDH genes. Following NaCl stress, the expression of Fd-GOGAT and NADH-GOGAT in the leaves of black wolfberry was downregulated with increasing time and NaCl concentration; in the roots, Fd-GOGAT and NADH-GOGAT were upregulated by 1.79-fold and 1.40-fold, respectively, 12 h after severe NaCl stress. GS2 and GS1.1 are highly expressed in leaves and roots, respectively, and their expression is significantly upregulated under NaCl stress. The expression of GDH in leaves is downregulated under salt stress, whereas in roots, the expression of NADP-GDH and GDH2 is upregulated under NaCl stress. C2H2-63, a key transcription factor regulating nitrogen assimilation in black wolfberry under salt stress, is likely to promote nitrogen assimilation through its upregulated expression. Additionally, seven positively selected sites (p.Glu220, p.Ala388, p.Ala880, p.Ser921, p.Leu1319, p.Ser1350, and p.Ser1570) were found in the Fd-GOGAT protein of black wolfberry. Compared to Ningxia wolfberry (L. barbarum), these mutation sites enhance the affinity of Fd-GOGAT for its substrate Glu, which helps to increase the catalytic efficiency of Fd-GOGAT in black wolfberry under salt stress. In conclusion, the adaptation of salt stress-related nitrogen assimilation genes in black wolfberry involves both gene expression regulation and adaptive evolution. Enhancing the GS/GOGAT pathway under salt stress is a primary strategic choice for nitrogen assimilation in black wolfberry.