Resistant plants can often quickly initiate salicylic acid (SA) production when they detect infection by a biotrophic pathogen. This leads to various downstream responses, including reactive oxygen species (ROS) burst, pathogenesis-related protein expression, and hypersensitive response. On the other hand, jasmonic acid (JA) and ethylene (ET) production and JA/ET-dependent defence responses are most commonly induced in response to necrotrophic pathogens. However, the interaction of plant host and hemibiotrophic pathogen is still not as well understood. The model plant Arabidopsis thaliana exhibits non-host resistance to Leptosphaeria maculans, a hemibiotrophic fungal pathogen that causes blackleg disease in Brassica crops. In this study, profile changes in the transcriptome and metabolome, and in the expression pattern of multiple defence-related pathways were assessed in Arabidopsis upon inoculation with L. maculans. Arabidopsis initiated numerous responses that enhanced the cell wall barrier, both physically and chemically. However, uncontrolled cell death caused by excessive hydrogen peroxide production broke the robust defence line as a whole. Arabidopsis was found to deploy active control of the production of SA, JA, ET and abscisic acid over the critically important first 3 days after inoculation. These responses likely enabled plants to quickly establish a robust defence line. It also maintained the delicate balance between ROS production and cell death development. The dynamic defence mechanism characterized in this study provides a successful strategy for Arabidopsis against L. maculans and (potentially) other hemibiotrophic fungal pathogens.
