PhD Student University of Florida Gainesville, Florida
Body of Abstract: Plants have evolved a large number of cell-surface receptor-like kinases (RLKs) and receptor-like proteins (RLPs) to perceive and transduce extracellular signals. RLKs are activated by ligand binding to their extracellular domains, followed by auto- or trans-phosphorylation in the cytoplasmic kinase domains, which recruit downstream signaling partners. BRASSIOSTEROID INSENSITIVE1-ASSOCIATED KINASE (BAK1), a member of the leucine-rich repeat RLK (LRR-RLK) family, is a shared signaling hub that interacts with other receptors and modulates distinct biological responses in both plant growth and development. It is recently proposed that BAK1 signaling specificity is achieved by specific and differential phosphorylation. Extracellular NAD(P) [eNAD(P)] is an emerging SAR signal. Through phosphoproteomics, we identified novel phosphorylation sites in BAK1 that were induced by eNAD(P) both in vitro and in vivo in Arabidopsis. Notably, these phosphorylation sites are not required for PAMP-triggered immunity (PTI). Conversely, eNAD(P)-induced resistance and SAR are not impaired in BAK1 C-terminal phosphor-deficient mutants with compromised PTI. Our finding highlights the hypothesis that BAK1 maintains signaling specificity in a phosphorylation-dependent manner and provides insights into the activation mechanisms of broad RLKs and RLPs.