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 CaCl2 and 50 mM KCl.
The purified peptide at 40 µM did not inhibit three different a-amylase
enzymes. Aeukaryotic 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.
