Sarah Bronwen Rees

Isolation and characterisation of plant defensins from seeds of Asteraceae, Fabaceae, Hippocastanaceae and Saxifragaceae

From seeds of Aesculus hippocastanum, Clitoria ternatea, Dahlia merckii and Heuchera sanguinea five antifungal proteins were isolated and shown to be homologous to plant defensins previously characterised from radish seeds and γ‐thionins from Poaceae seeds. Based on the spectrum of their antimicriobial activity and the morphological distortions they induce on fungi the peptides can be divided into two classes. The peptides did not inhibit any of three different α‐amylases.

A Novel Family of Small Cysteine-rich Antimicrobial Peptides from Seed of Impatiens balsamina Is Derived from a Single Precursor Protein

Four closely related peptides were isolated from seed of Impatiens balsamina and were shown to be inhibitory to the growth of a range of fungi and bacteria, while not being cytotoxic to cultured human cells. The peptides, designated Ib-AMP1, Ib-AMP2, Ib-AMP3, and Ib-AMP4, are 20 amino acids long and are the smallest plant-derived antimicrobial peptides isolated to date. The Ib-AMPs (I. balsamina antimicrobial peptides) are highly basic and contain four cysteine residues which form two intramolecular disulfide bonds. Searches of protein data bases have failed to identify any proteins with significant homology to the peptides described here. Characterization of isolated cDNAs reveals that all four peptides are encoded within a single transcript. The predicted Ib-AMP precursor protein consists of a prepeptide followed by 6 mature peptide domains, each flanked by propeptide domains ranging from 16 to 35 amino acids in length. Such a primary structure with repeated alternating basic mature peptide domains and acidic propeptide domains has, to date, not been reported in plants.

Cloning and characterization of a cDNA encoding an antimicrobial chitin-binding protein from amaranth, Amaranthus caudatus

A cDNA clone encoding an antimicrobial chitin-binding protein from amaranth (Amaranthus caudatus L.) was isolated using a cDNA library constructed from near-mature seed poly(A)+ mRNA. The deduced amino acid sequence of the cDNA clone encodes a predicted polypeptide of 86 amino acids. This polypeptide has three distinct domains: an amino-terminal putative signal peptide (25 amino acids), a domain corresponding to the mature protein (30 amino acids), and a carboxyl-terminal propeptide (31 amino acids) containing a putative N-glycosylation site. The encoded protein differs from all known members of the family of chitin-binding proteins. Transcripts of the expected size (650 bp) are present in developing seeds but not in roots, leaves or stressed leaves.