Primers used in this study.

Plant endogenous peptides are crucial for diverse aspects of plant physiology. Among them, C-TERMINALLY ENCODED PEPTIDEs (CEPs) have recently emerged as important regulators of plant growth and stress responses. CEPs are divided into two major subgroups: group I CEPs and the less studied group II CEPs. We recently demonstrated that group I CEPs coordinate cell surface receptor-mediated immunity with nitrogen status in Arabidopsis thaliana (hereafter Arabidopsis). To mount full group I CEP responsiveness, the three phylogenetically related CEP RECEPTOR 1 (CEPR1), CEPR2 and RECEPTOR-LIKE KINASE 7 (RLK7) are required. Here, we provide evidence that biotic stress induces expression of the group II CEP peptide CEP14. CEP14 and the related CEP13 and CEP15 trigger hallmark immune signalling outputs in a proline hydroxylation pattern-dependent manner in Arabidopsis. Genetic data indicate that group II CEP members contribute to cell surface receptor-mediated immunity against bacterial infection. We further show that group II CEP perception primarily depends on CEPR2. Our work provides new insights into CEP function during biotic stress and sheds new light on the complexity of sequence-divergent CEP signalling mediated by specific endogenous receptors.