THESEUS1 positively modulates plant defense responses against Botrytis cinerea through GUANINE EXCHANGE FACTOR4 signaling.

The plant cell wall is an important interface for sensing pathogen attack and activating signaling pathways that promote plant immune responses. THESEUS1 (THE1) acts as a sensor of cell wall integrity that controls cell elongation during plant growth. However, no specific role for THE1 in plant defense responses has been reported. Here, we found that THE1 interacts with GUANINE EXCHANGE FACTOR4 (GEF4) and that both proteins play regulatory roles in plant resistance to the necrotrophic fungus Botrytis cinerea. Genetic analysis showed that THE1 and GEF4 function in the same genetic pathway to mediate plant defense responses. In addition, using transcriptome analysis, we identified various genes (such as defense-related, secondary metabolite-related, and transcription factor genes) that are likely downstream targets in the THE1-GEF4 signaling pathway. Our results suggest that THE1 functions as an upstream regulator of GEF4 signaling to positively regulate defense responses against B. cinerea in Arabidopsis.