The NIP Genes in Sugar Beet: Underlying Roles in Silicon Uptake and Growth Improvement

Silicon (Si) can stimulate plant growth and stress resistance. This study aimed at elucidating the physiological responses and molecular characterization of different NIP (nodulin 26-like intrinsic protein) genes in sugar beet. The addition of exogenous Si increased plant biomass and Si concentration in the root and shoot, implying that increased Si uptake has beneficial effects on sugar beet. The quantitative gene expression analysis showed a significant upregulation of the BvNIP5–1 gene in roots, while the BvNIP1–1 , BvNIP6–1 , BvNIP7–1, and BvNIP-type were unchanged following Si supplementation. It suggests that BvNIP5–1 is one of the genes localized in the plasma membrane responsible for Si uptake in sugar beet. Besides, the BvNIP5–1 gene contained promoter, transcription start site, transcription binding site, and PolyA at 800 bp, 528 bp, 557 bp, and 1637 bp, respectively. The MEME results further revealed the association of three motifs related to major intrinsic protein (MIP). In the phylogenetic tree, the BvNIP5–1 showed a close association with CqNIP5–1 , AnNIP2–1 and SoNIP5–1 . Interactome analysis showed functional partnership of aquaporin SIP1–2 and SIP2–1 genes with NIP genes in sugar beet. In addition, BvNIP5–1 possessed close association with several functional partners ( BOR1 , BOR1 , NodGS , SIP1A , ACR3 ) and co-expressed genes (i.e., AtNIP5–1 , AtBOR1 , AtNodGS , AtSIP1A , AtACR3 ) of Arabidopsis thaliana mainly responsible for boron, arsenite, and aquaporin transport activity. NIP promoters revealed cis -regulatory elements linked to auxin, salicylic acid, and methyl jasmonate-responsive factors. These findings may advance our understanding of Si transporters underlying growth and stress tolerance in sugar beet.