The control of fungal and bacterial plant diseases mainly relies on the application of mineral and chemical fungicides/bactericides, which are considered to be environmental pollutants and toxic to humans. Moreover, the prolonged use of bactericides and antibiotics has led to the development of resistance among pathogens, as well as an increase in environmental and health threats. Therefore, the development of non-toxic and non-polluting treatments to control plant diseases has been the focus of extensive research in agriculture. Synthetic antimicrobial peptides have recently received extensive attention as the potential alternatives to other conventional methods in terms of their strong broad-spectrum antimicrobial activity. In vitro assays using various chemically synthesized peptides showed that the broad-spectrum peptide thanatin derived from the spined soldier bug (Podisus maculiventris (Say)) had the greatest potential for eliminating aflatoxigenic fungi. However, the antibacterial effect of thanatin against bacterial plant pathogens was less studied so far. The thanatin encoding sequence was codon optimized for expression in Pichia pastoris. This coding sequence cloned into P. pastoris expression vector pPICZαA and used for synthetizing the recombinant thanatin. Then, antibacterial activities of the constructed peptide were studied under in vitro and in vivo condition. The result showed that, all construction, cloning and expression processes were successfully performed in yeast. The results of the MIC and MBC tests showed that the growth rate of the majority of bacterial plant pathogens including gram-negative and gram-positive bacteria was inhibited by recombinant thanatin under in vitro conditions. MIC values for different bacterial isolates ranged from 0.016 to 2.048, while the MBC values for the same bacterial isolates were determined to be between 0.064 and 4.096 μg/mL. These amounts were significantly lower than the MIC and MBC values obtained by applying copper oxychloride. The application of 4.09 μg/mL of recombinant thanatin against rice leaf blight splendidly controlled this bacterial disease under greenhouse conditions. However, this promising antimicrobial peptide requires further investigation for the development of novel molecules for the control of plant pathogens.

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