Quantitative and functional posttranslational modification proteomics reveals that TREPH1 plays a role in plant touch-delayed bolting

Significance Plants respond to a delicate force signal, such as a light touch, similar to animal neural systems, as demonstrated by thigmotropism, thigmonastic movement, and thigmomorphogenesis. To understand the force-signaling networks, we applied stable isotope labeling in Arabidopsis (SILIA)-based quantitative posttranslational modification proteomics to assess protein phosphorylation changes in Arabidopsis subjected to 40-second cotton-swab touch, identified 4,895 nonredundant phosphopeptides, 579 of which are previously unreported phosphosites derived from 509 phosphoprotein groups, and identified 24 TOUCH-REGULATED PHOSPHOPROTEIN (TREPH) groups. Molecular biological, genetic, and bioinformatic analyses revealed that the previously uncharacterized TREPH1 protein is required for the bolting-delay aspect of the Arabidopsis touch response. These studies suggest that protein phosphorylation and the TREPH1 protein are critical for the mechanotransduction pathway leading to an aspect of plant thigmomorphogenesis.