Trichoderma root colonization in maize triggers epigenetic changes in genes related to the jasmonic and salicylic acid pathways that prime defenses against Colletotrichum graminicola leaf infection.

Beneficial interactions between plant roots and Trichoderma species lead to both local and systemic enhancements of the plant immune system through a mechanism known as priming of defenses. Previously, we have reported a number of genes and proteins that are differentially regulated in distant tissues of maize plants following inoculation with Trichoderma atroviride. To further investigate the mechanisms involved in the systemic activation of plant responses, here we have further evaluated the regulatory aspects of a selected group of genes when priming is triggered in maize plants. Time-course experiments from the beginning of the interaction between T. atroviride and maize roots followed by leaf infection with Colletotrichum graminicola allowed us to identify a gene set regulated by priming in the leaf tissue. In the same experiment, phytohormone measurements revealed a decrease in jasmonic acid concentration while salicylic acid increased at 2 d and 6 d post-inoculation. In addition, chromatin structure and modification assays showed that chromatin was more open in the primed state compared with unprimed control conditions, and this allowed for quicker gene activation in response to pathogen attack. Overall, the results allowed us to gain insights on the interplay between the phytohormones and epigenetic regulatory events in the systemic and long-lasting regulation of maize plant defenses following Trichoderma inoculation.