Genome-wide Identification and Characterization of the STR Gene in Dendrobium officinale

Abstract Alkaloids are the main active ingredients in the traditional Chinese medicine Dendrobium spp. Terpenoid indole alkaloids (TIAs), a class of secondary metabolites with a nitrogen heterocyclic structure, are low in content and difficult to synthesize chemically. Strictosidine synthetase (STR) is a key enzyme that catalyzes the Pictet-Spengler reaction of TIAs. However, the molecular characteristics and enzymatic properties of STR proteins in Dendrobium officinale remain unclear. Through bioinformatics analysis, we systematically studied the protein purification and catalytic activity of DoSTR. We initially identified eight STR homologous genes in D. officinale. Members of the DoSTR family vary in molecular weight, theoretical isoelectric point, and subcellular localization. Cis-acting element analysis of the DoSTR promoter revealed the presence of multiple elements involved in phytohormone response and biotic and abiotic stress. Phylogenetic tree and homology alignment revealed that DoSTR proteins are more closely related to STR proteins of Dendrobium huoshanense;however, DoSTR are evolutionarily distant from plant STR proteins with characterized functions, such as CrSTR, RvSTR, and RsSTR. Conservative motif analysis revealed a conserved motif in the STR sequence. The Glu309 residue, which is associated with catalysis, is not conserved. Using qRT-PCR, the expression pattern of DoSTR was found to be spatially specific. Through transient expression in tobacco, DoSTR8 was shown to localize to cell membranes. The DoSTR8 recombinant protein was successfully expressed in E. coli using prokaryotic expression and purified. The findings of this study may provide valuable insights into further research on the function of the STR gene family in D. officinale.