Fusion Partner and ER-Retention Signal Are Associated with Distinct Host Proteomic and Metabolic Responses During Interleukin-15 Production in Nicotiana benthamiana

Plant molecular farming has emerged as a promising platform to produce recombinant biopharmaceuticals. The expression of foreign proteins changes the host proteome and metabolome, and these changes might have an effect on the accumulation of recombinant proteins. In this study, we investigated how fusion partners and ER-retention strategies influence host responses during transient production of recombinant human interleukin-15 (IL-15) in Nicotiana benthamiana. Four IL-15 constructs carrying either an 8 × His tag or an IgG1 Fc fusion, with or without an N-terminal signal peptide and C-terminal SEKDEL motif (KD), were compared at 4 days post-infiltration. Western blot analysis detected IL-15 only in the Fc-fusion constructs. Plants expressing IL15-Fc accumulated more antioxidant enzymes and phenylpropanoid-derived phenolics. Expression of IL15-Fc with the SP/KD construct showed increased abundance of proteins involved in protein folding and translation, together with reduced representation of secondary metabolic pathways. Overall, the results demonstrate that fusion partner and SP/KD targeting strategy jointly shape the host response to recombinant IL-15 expression and should therefore be evaluated together during construct design for plant molecular farming.