Abstract
Tyrosine sulfation is a posttranslational modification found in peptides and proteins synthesized by the secretory pathway in most eukaryotes. In plants, this modification is critical for the biological activities of a subset of peptide hormones such as PSK and PSY1. To investigate the mechanisms of tyrosine sulfation in plants, we purified TPST activity from microsomal fractions of Arabidopsis cells and identified a 62-kD protein that specifically interacts with the sulfation motif of PSY1 precursor peptide. AtTPST is expressed throughout the plant body, and the highest levels of expression are in the root apical meristem (RAM). A loss-of-function mutant of Arabidopsis displayed a marked dwarf phenotype accompanied by stunted roots, pale green leaves, reduction in higher order veins and early senescence. Interestingly, root growth defect in tpst mutant was not recovered by the addition of PSK and PSY1 in the medium, suggesting that as-yet-unknown sulfated peptide is required for normal root growth. We are searching for this peptide by in silico gene screening approach.
