The ATP Binding Cassette (ABC) Transporter Gene Family in Lotus (Nelumbo Adans.): Genome-Wide Survey, Characterization and Gene Expression Profile

ABC transporters (ATP-binding cassette transporters) constitute one of the largest known protein families and are widely distributed in plants. Their primary function involves utilizing energy derived from ATP hydrolysis to transport substrates across membranes against concentration gradients. These transporters play crucial roles in the translocation and accumulation of metabolites, stress tolerance, disease resistance, and plant defense. Lotus is an important traditional Chinese medicinal herb and contains active ingredients primarily composed of secondary metabolites, whose transport and accumulation require the involvement of ABC transporters. However, the function of these ABC transporters remains unexplored in lotus. In this study, 122 ABC transporter genes were predicted within the lotus genome. We identified 1~15 conserved motifs among the NnABC proteins and most of them were stable proteins predominantly located on the plasma membrane with ExPASy-ProtParam, ProComp and WoLF PSORT analysis. Phylogenetic tree analysis revealed that the lotus ABC transporter gene family could be divided into eight subfamilies, from ABCA to ABCI, and the evolution was predominantly driven by purifying selection. Comparative transcriptome analysis between the cultivar 'Yindu Zhimi' with orange-reddish stamen and 'Weishan Hong' with yellowish stamen, along with quantitative real-time PCR results, showed that the <i>NnABCG25</i> gene is highly specifically expressed in the orange-reddish stamen. Molecular docking demonstrated that NnABCG25 has a stable affinity for lycopene, β-carotene and β-apocarotenal, suggesting its potential involvement in the transport of carotenoids in the stamen. These findings expand our understanding of the role of ABC transporters in the transport and accumulation of carotenoids, as well as providing a valuable reference for research on the ABC transporter gene family in other plants.