Opposing Roles of Plant Laticifer Cells in the Resistance to Insect Herbivores and to Fungal Pathogens

Abstract More than 12,000 plant species (ca. 10% of flowering plants) exude latex when their tissues are injured. Latex is produced and stored in specialized cells named “laticifers”. Laticifers conform a tubing system constituted of rows of elongated cells that branch and form an internal network of cells encompassing the entire plant. Laticifers constitute a recent evolutionary achievement for ecophysiological adaptation to specific natural environments, however the fitness benefit to the plant still remains to be proven. The identification of Euphorbia lathyris mutants (pil mutants) deficient in laticifer cells or latex metabolism, and therefore compromised in latex production, allowed testing the importance of laticifers in pest resistance. We provide genetic evidence indicating that laticifers represent a cellular adaptation for an essential defense strategy to fend off arthropod herbivores with different feeding habits such as Spodoptera exigua and Tetranychus urticae. In marked contrast, we also unveiled that lack of laticifer cells results in gaining a complete resistance to the fungal pathogen Botrytis cinerea. Thereafter, a latex-derived factor required for conidia germination in the leaf surface was identified. This factor promoted disease susceptibility enhancement even in the non-latex bearing plant Arabidopsis. We speculate on the role of laticifers in the co-evolutionary arms race between plants and their enemies.