Tomato PEPR1 ORTHOLOG RECEPTOR-LIKE KINASE1 Regulates Responses to Systemin, Necrotrophic Fungi, and Insect Herbivory.

Endogenous peptides regulate plant immunity and growth. Systemin, a peptide specific to the Solanaceae, is known for its functions in plant responses to insect herbivory and pathogen infections. Here, we describe the identification of the tomato () PEPR1/2 ORTHOLOG RECEPTOR-LIKE KINASE1 (PORK1) as the TOMATO PROTEIN KINASE1b (TPK1b) interacting protein and demonstrate its biological functions in systemin signaling and tomato immune responses. Tomato RNA interference (RNAi) plants with significantly reduced expression showed increased susceptibility to tobacco hornworm (), reduced seedling growth sensitivity to the systemin peptide, and compromised systemin-mediated resistance to Systemin-induced expression of (), a classical marker for systemin signaling, was abrogated in RNAi plants. Similarly, in response to systemin and wounding, the expression of jasmonate pathway genes was attenuated in RNAi plants. TPK1b, a key regulator of tomato defense against and , was phosphorylated by PORK1. Interestingly, wounding- and systemin-induced phosphorylation of TPK1b was attenuated when expression was suppressed. Our data suggest that resistance to and is dependent on PORK1-mediated responses to systemin and subsequent phosphorylation of TPK1b. Altogether, PORK1 regulates tomato systemin, wounding, and immune responses.