Genome-Wide Analysis of the Aquaporin Gene Family Reveals the Role of NnPIP2-7 in Conferring Salt Tolerance in Lotus (Nelumbo nucifera Gaertn.)

Salt stress represents a major constraint on the productivity of lotus (Nelumbo nucifera), an aquatic crop of significant ornamental, nutritional, and medicinal value. Although aquaporins (AQPs) are key regulators of plant water and solute homeostasis, the genomic organization and stress-responsive functions of this gene family in lotus remain largely uncharacterized. In this study, a total of 32 NnAQP genes were identified in the lotus genome and classified into five subfamilies. Segmental duplication was identified as the primary driver of family expansion under strong purifying selection. Expression profiling revealed broad transcriptional activity across various tissues, and qRT-PCR analysis demonstrated that NnPIP2-7 was significantly and sustainedly induced under salt stress. Subcellular localization confirmed that NnPIP2-7 is targeted to the plasma membrane. Heterologous overexpression of NnPIP2-7 in Arabidopsis thaliana significantly improved seed germination and primary root elongation under saline conditions. Crucially, transgenic plants exhibited enhanced osmotic adjustment and elevated antioxidant capacity, resulting in reduced oxidative damage compared to wild-type plants. These findings establish the evolutionary trajectory of the lotus AQP family and demonstrate the core regulatory role of NnPIP2-7 in plant salt stress adaptation.