Cell-to-cell communication by excreted peptides is pivotal for many regulatory mechanisms of living organisms. For example, plant peptide hormones (PPHs) are an important class of signaling and regulating molecules for plant growth, developmental processes or defense responses. Whereas details of these mechanisms have been established for simple peptides, a major fraction of PPHs are chemically modified that are more difficult to obtain and study. Prominent plant-related posttranslational modifications (PTMs) are proline hydroxylation, tyrosine sulfation, and hydroxyproline arabinosylation. As some of these chemical modifications are poorly compatible with current synthetic approaches, details of their interaction with their corresponding receptors, such as leucine-rich repeat receptor-like kinases (LRR-RLKs), are yet to be elucidated. As such, effects of this peptide-receptor interaction for intracellular signaling pathways remain poorly understood.