PURIFICATION, CHARACTERIZATION AND CDNA CLONING OF AN ANTIMICROBIAL PEPTIDE FROM MACADAMIA-INTEGRIFOLIA

An antimicrobial peptide with no significant amino acid sequence simil arity to previously described peptides has been isolated from the nut kernels of Macadamia integrifolia. The peptide, termed MiAMP1, is high ly basic with an estimated pI of 10.1, a mass of 8.1 kDa and contains 76 amino acids including 6 cysteine residues. A cDNA clone containing the entire coding region corresponding to the peptide was obtained. Th e deduced amino acid sequence of the cDNA indicated a 26-amino-acid si gnal peptide at the N-terminus of the preprotein. Purified MiAMP1 inhi bited the growth of a variety of fungal, oomycete and gram-positive ba cterial phytopathogens in vitro. Some pathogens exhibited close to 100 % inhibition in less than 1 mu M peptide (5 mu g/ml). Antimicrobial ac tivity was diminished against most, but not all, microbes in the prese nce of calcium and potassium chloride salts (1 mM and 50 mM, respectiv ely). MiAMP1 was active against bakers yeast, was inactive against Esc herichia coli and was non-toxic to plant and mammalian cells. Analysis of genomic DNA indicated that MiAMP1 was encoded on a single copy gen e containing no introns. The MiAMP1 gene may prove useful in genetic m anipulations to increase disease resistance in transgenic plants.