Flg22 is an artificially synthesized 22-amino-acid peptide derived from the conserved N-terminal region of bacterial flagellin, playing a crucial role in regulating plant immune responses. Due to the high cost of artificially synthesized flg22 short peptides and limitations for large-scale application, this study aimed to determine the suitable conditions for prokaryotic induction expression of the flg22 protein and to verify its function, thereby determining whether it could replace the commercially used flg22 short peptides. In this study, the pET32a-flg22 prokaryotic expression vector was synthesized, and we then compared protein expression efficiency under induction at 28 ℃ and 37 ℃. Additionally, we detected the dynamic burst of reactive oxygen species (ROS) in cassava treated with flg22 peptides and flg22 proteins at different concentrations to validate the functions. The results indicated that 28 ℃ was the optimal induction temperature for inducing flg22 protein expression. ROS measurements showed that within a specific concentration range, the peak intensity of ROS increased with the increase in flg22 protein concentration. Furthermore, after spraying cassava leaves with 60 μg/mL and 600 μg/mL of flg22 recombinant proteins, as well as 2.27 μg/mL of flg22 peptides, for three days, we inoculated plants with the pathogen Xam (Xanthomonas axonopodis pv. manihotis, Xam). Compared to treatment with sterile water, both flg22 protein and flg22 peptide treatments showed significant antibacterial effects against Xam in cassava plants, with the 60 μg/mL and 600 μg/mL flg22 protein treatments showing notably stronger antibacterial activity than the flg22 peptide. The results preliminarily identified the prokaryotic expression conditions of flg22 recombinant protein and verified that its function in inducing plant defense responses is consistent with that of the peptide, providing a theoretical basis for substituting commercial peptides with flg22 recombinant protein.