Endophytic Streptomyces griseorubens MEPSL1 from sweetpotato promotes plant growth and enhances γ-tocopherol accumulation

ABSTRACT Endophytic actinomycetes are known to promote plant growth and improve crop nutritional quality through nutrient mobilization and secondary metabolite production. In this study, a multifunctional actinomycete strain was isolated from sweetpotato ( Ipomoea batatas (L.) Lam.) and identified as Streptomyces griseorubens MEPSL1. Functional assays and genome analysis revealed that MEPSL1 exhibits several plant growth-promoting traits, including nitrogen fixation, phosphate solubilization, indole-3-acetic acid and siderophore production, 1-aminocyclopropane-1-carboxylate deaminase activity, and secretion of protease, amylase, and carboxymethyl cellulose-degrading activity. Inoculation of sweetpotato plants with MEPSL1 significantly increased the γ-tocopherol content in leaves, with HPLC analysis showing an increase of 38.31 μg g −1 dry weight compared to the control. Quantitative real-time PCR analysis confirmed the upregulation of four genes associated with tocopherol biosynthesis following treatment. Metabolite profiling also detected the presence of metabolites linked to tocopherol biosynthesis, suggesting a potential association in MEPSL1 cultures and a possible contribution to enhanced γ-tocopherol accumulation. These findings indicate that MEPSL1 can serve as an effective bioinoculant for improving both plant growth and the nutritional composition of sweetpotato leaves, with potential applications in sustainable agriculture and functional food development. IMPORTANCE Streptomyces species are widely distributed in soils and plant tissues and are valued for their ecological safety and diverse biological functions. Here, we describe a multifunctional endophytic actinomycete, Streptomyces griseorubens MEPSL1, isolated from sweetpotato. This strain exhibits multiple growth-promoting traits and significantly increases γ-tocopherol accumulation in sweetpotato leaves, accompanied by the induction of key biosynthetic genes. Our findings highlight the role of endophytic actinomycetes in improving both crop performance and nutritional quality and point to their potential use in sustainable biofortification strategies.