Peptide signals for plant defense display a more universal role

Hydroxyproline-rich systemins (HypSys) are small defense signaling glycopeptides found within the Solanaceae family that until recently were thought to only induce defense genes to herbivore attack. The glycopeptides are processed from larger proproteins with up to 3 different glycopeptides being processed out of a single precursor protein. A conserved central hydroxyproline motif within each HypSys is the site of pentose sugar attachment. Recently, it was found that in Petunia hybrida, these defense signaling glycopeptides did not induce protease inhibitor but instead, increased levels of defensin, a gene that is involved in pathogen attack. More recently, a HypSys peptide was isolated from Ipomoea batatas (sweet potato) of the Convolvulaceae family and found to induce sporamin. The proprotein precursor contained six putative peptide signals and had a propeptidase processing region with homology to solanaceous proHypSys. Thus, the HypSys defense peptides are no longer confined to defense against herbivory or exclusivity to the Solanaceae family, redefining both function and dispersion.