Sucrose-Activated TOR and phyA Signaling Alleviates Shade-Mediated Inhibition of Leaf Development in Arabidopsis

To investigate how the sucrose-TOR signaling pathway regulates phyA, we conducted LC-MS/MS analysis to identify phosphorylation sites on phyA. In vivo, the phyA protein was immunoprecipitated from 35S::PHYA-YFP/phyA-211 seedlings treated with shade and 30 mM sucrose for 6 hours. In vitro, we used recombinant phyA protein purified from insect cells as the substrate and endogenous TOR complex immunoprecipitated from the 35S::LST8-1-FLAG transgenic line as the kinase source. Phosphopeptide enrichment and LC–MS/MS analysis of the in vitro reaction were performed.