2. Synthesis and Signal Transduction of PSK Peptide 2.1. Biosynthesis of the PSK Peptide The majority of peptides, which are derived from precursor proteins, go through a series of posttranslational modifications, including tyrosine sulfation, proline hydroxylation, glycosylation, and processing by proteases, before becoming active molecules that ultimately cause physiological responses [9,10]. Seven precursor genes (AtPSK1-AtPSK7) encoding PSK have been identified in Arabidopsis.
