Cloning and expression analysis of NoSTR1 gene of Nauclea officinalis

【Objective】 This study aimed to clone the strictosidine synthase （STR） gene of Nauclea officinalis （NoSTR1） and analyze its tissue-specific expression difference， providing theoretical basis for elucidating pathways and mechanisms of indole alkaloid synthesis in Nauclea officinalis. 【Method】 The NoSTR1 gene was identified based on transcriptome data of Nauclea officinalis and cloned， and the physicochemical properties， structure， and phylogeny of NoSTR1 protein were analyzed. The roots， stems， and leaves of Nauclea officinalis were used as experimental materials. Real-time fluorescence quantitative PCR was employed to detect the relative expression of NoSTR1 gene in different tissues of Nauclea officinalis， and high performance liquid chromatography （HPLC） was used to detect the content of strictosamide， one of indole alkaloids， in different tissues of Nauclea officinalis. 【Result】 The cloned NoSTR1 gene contained a coding sequence （CDS） of 1032 bp， encoding 344 amino acid residues. The molecular formula of NoSTR1 protein was C₁₇₂₀H₂₆₃₁N₄₃₁O₅₁₃S₇， with a molecular weight of 37779.81 Da， theoretical isoelectric point of 5.00， indicating that it was a stable hydrophilic protein with a signal peptide without transmembrane regions. In the secondary structure of NoSTR1 protein， α-helix accounted for 18.37%， β-sheet 29.15%， and random coils 52.48%； tertiary structure predictions indicated that it was a typical 6-bladed β-propeller fold protein. The NoSTR1 protein had a conserved domain of Str_synth superfamily. Phylogenetic tree analysis showed that the NoSTR1 protein was clustered in the same clade with STR proteins of Gelsemium sempervirens， Ophiorrhiza japonica， and Ophiorrhiza pumila， showing a close relationship. The NoSTR1 gene was expressed in roots， stems， and leaves of Nauclea officinalis， with the highest expression observed in stems， and the lowest in leaves. The strictosamide content of Nauclea officinalis was the highest in stems and the lowest in leaves， exhibiting a similar change pattern with the relative expression of NoSTR1 gene. 【Conclusion】 The encoded proteins of NoSTR1 gene contains a conserved domain， which is specifically for STR protein Str_synth superfamily. The relative expression of NoSTR1 gene in different tissues of Nauclea officinalis shows a similar change pattern with strictosa-mide content， indicating that the NoSTR1 gene is the key candidate gene of indole alkaloid synthesis pathways of Nauclea officinalis.