Genome-wide characterization of the NRT1 family members under cold stress in Coconut (Cocos nucifera L.)

Coconut is an important oil crop in tropical areas, and it plays various important roles in industry. Nitrogen is a crucial mineral nutrient for plant development, and the absorption and transport of nitrate nitrogen, facilitated by NRT1s have been extensively studied in various crops. However, research on nitrogen absorption and stress resistance mediated by the NRT1 gene family has not yet been undertaken in coconut. In this study, multiple bioinformatics tools were employed to identify 67 members of the NRT1 gene family in dwarf coconuts, which can be categorized into 8 subfamilies. The analysis also determined the NRT1 genes' molecular weight, chromosome distribution, subcellular localization, transmembrane structure, and conserved structural domains. In addition, it was discovered that the proline concentration in dwarf coconut leaves significantly increased after 8 h and 7 days of cold treatment. Transcriptome and qPCR analysis revealed that after 7 days of cold stress, the expression levels of the coconut CnNRT1 genes generally decreased significantly. This suggests that cold stress may inhibit the absorption and transport of nitrate nitrogen in coconuts. In a combined examination of tall and dwarf coconut varieties, it was observed that CnNRT1.5, CnNRT1.8, CnNRT1.13, and CnNRT1.17 genes responded promptly to cold stress signals after 8 h, showing heightened expression levels in various plant parts such as roots, stems, floral organs, and fruit peels. This observation suggests a potential involvement of nitrate nitrogen, regulated by CnNRT1 genes, in the coconut's ability to adapt to cold stress. This further suggests that nitrate nitrogen mediated by CnNRT1s may participate in the coconut's adaptation to cold stress. These results provide important foundational information for studying the function of NRT1 genes in coconuts and their research on the molecular mechanisms of coconut's cold tolerance.