A family of antimicrobial peptides is produced by processing of a 7S globulin protein in Macadamia integrifolia kernels

A new family of antimicrobial peptides has been discovered in Macadamia integrifolia. The first member of this new family to be purified from nut kernels was a peptide of 45 aa residues, termed MiAMP2c. This peptide inhibited various plant pathogenic fungi in vitro. cDNA clones corresponding to MiAMP2c encoded a 666 aa precursor protein homologous to vicilin 7S globulin proteins. The deduced precursor protein sequence contained a putative hydrophobic N-terminal signal sequence (28 aa), an extremely hydrophilic N-proximal region (212 aa), and a C-terminal region of 426 aa which is represented in all vicilins. The hydrophilic portion of the deduced protein contained the sequence for MiAMP2c as well as three additional segments having the same cysteine spacing pattern as MiAMP2c. Each member of the MiAMP2 family (i.e. MiAMP2a, b, c and d) consisted of approximately 50 amino acids and contained a C-X-X-X-C-(10-12)X-C-X-X-X-C motif. Subsequent isolations from seed exudates led to the purification of the predicted family members MiAMP2b and 2d, both of which also exhibited antimicrobial activity in vitro. These results suggest that some vicilins play a role in defence during seed germination

Evolution of pathotypes of Puccinia helianthi on sunflower in Australia

Sunflower rust caused by Puccinia helianthi is a major problem in sunflower production in Australia. The disease can be effectively controlled through the use of resistant hybrids but the commercial life of these is often short, due to the evolution of new pathotypes of the fungus. Since 1978,23 pathotypes have been recognised, mostly from commercial crops. Possible pathways for the evolution of these pathotypes are proposed. Almost all pathotypes identified since 1986 trace to a common progenitor, Aus4. Avirulence/virulence patterns of many pathotypes suggest that sexual recombination may be acting to generate new pathotypes, but the sexual stages of the fungus are rarely seen in the field. It is assumed that bursts of evolution occur in seasons that favour completion of the sexual cycle, and that mutation contributes steadily to the development of new virulence genes in the population of P helianthi

An antimicrobial peptide from the Australian native Hardenbergia violacea provides the first functionally characterised member of a subfamily of plant defensins

An antimicrobial peptide (HvAMP1) was isolated from seeds of the Australian native legume Hardenbergia violacea (Schneev.) Stearn. The peptide is 47 amino acid residues in length, contains 8 cysteines, and has a molecular weight of 5392 and a predicted pI of 10.41. HvAMP1 inhibited the growth of several plant pathogenic fungi at concentrations as low as 1 μM in vitro and produced distinct hyphal distortion and increased branching. This antimicrobial activity was greatly diminished in the presence of 1 mM CaCl and 50 mM KCl. The purified peptide at 40 μM did not inhibit three different α-amylase enzymes. A eukaryotic cell-free translation system showed inhibition approaching 50% in the presence of ~100 μM of HvAMP1. The viability of plant and mammalian cells cultured in vitro was not adversely affected by concentrations of HvAMP1 as high as 40 mM. The amino acid sequence of HvAMP1 contained the consensus amino acids that define the plant defensin family of peptides. The HvAMP1 amino acid sequence showed 87% and 57% identity with the amino acid sequences deduced from cDNA sequences from defensins of Vigna unguiculata and Pisum sativum, respectively. Other plant defensin sequences showed less than 33% amino acid identity to the peptide. Therefore, HvAMP1 and the putative plant defensins of cowpea and pea define a distinct sequence subfamily of plant defensins which is at present limited to members of the Fabaceae. HvAMP1 is the first member of this subfamily to be purified and functionally characterised. The antimicrobial activity of HvAMP1 suggests a defensive role for this subfamily of peptides