Coronatine Subverts Tomato Immunity by Hijacking Hormonal Networks and Perturbing Physiological Homeostasis in Tomato Plants

Coronatine (COR) is a non-host-specific phytotoxin secreted by some pathogenic species of Pseudomonas syringae, which is known to be a chlorosis toxin that mediates the chlorosis symptoms of tomato bacterial speck disease. COR is a mimic of jasmonoyl isoleucine (JA-Ile), the conjugate of plant hormone jasmonic acid (JA) and isoleucine. By analyzing P. syringae DC3000 and mutants of PtoΔcor-, PtoΔCEL- and PtoΔCEL/cor- interacted with tomato plants, we demonstrate that, in tomato leaf tissues, COR is a multifunctional defense suppressor. COR and effectors from CEL (Conserved Effector Locus) play an overlapping or redundant role in inhibiting salicylic acid (SA) signaling pathway and callose deposition. In addition to inhibiting the SA pathway, COR-producing strains also manipulate host signaling pathways to promote parasitism by influencing JA, ethylene (ET), and other phytohormone pathways. COR also interferes with some important plant physiological processes such as photosynthesis and oxidation homeostasis. Further, our results also indicated that COR suppressed tomato defense to promote bacterial growth by both SA-dependent and SA-independent pathway in SlNPR1-RNAi plants. In addition, COR to promote bacterial growth is dependent on SlCOI1 in plants. Together, all results will provide a valuable resource for future to study the mechanisms of Pseudomonas syringae and tomato interaction.