CECROPIN A-DERIVED PEPTIDES ARE POTENT INHIBITORS OF FUNGAL PLANT-PATHOGENS

Cecropins are naturally occurring peptides that play an important role in the immune response of insects. Cecropin A-derived and cecropin A- melittin hybrid peptides, all smaller than the natural compound cecrop in A, were synthesized and tested for their ability to inhibit growth of several agronomically important fungal pathogens. We found that an 11-amino-acid sequence, corresponding to the N-terminal amphipathic al pha-helix domain of cecropin A, exhibited antifungal activity. Differe nces in susceptibility of the various pathogens were observed, Phytoph thora infestans being particularly sensitive to the shortened cecropin A peptides (IC50 = 2 X 10(-6) M). Biotoxicity of the shortest cecropi n A-derived peptide was variously affected by the presence of proteins extracted from leaves of tobacco and tomato plants, either total extr acts or intercellular fluids (ICFs). Overall, there was a greater tole rance to tomato protein extracts than to tobacco extracts, These findi ngs suggest that tobacco should not be used as a model for testing the possible protective effects of transgenically expressed, cecropin-bas ed genes. The feasibility of tailoring cecropin A genes to enhance cro p protection in particular plant/fungus combinations is discussed.