Exl1 from Pectobacterium activates a jasmonate-dependent immune network in Arabidopsis thaliana.

Bacterial expansins contribute to the virulence of diverse plant pathogens, yet their biological activity and molecular roles during host interactions remain to be elucidated. Expansin-like protein, Exl1, from phytopathogens from the genus Pectobacterium, activates defense responses in Arabidopsis thaliana involving production of reactive oxygen species (ROS), and the jasmonic acid (JA), ethylene (ET), and salicylic acid (SA) pathways, ultimately reducing disease symptoms upon subsequent infections with P. brasiliense and the fungus Botrytis cinerea. However, the target of Exl1 within the plant cell wall and the downstream pathways associated with these responses are yet to be identified. Here, we analyzed the transcriptomic profile of A. thaliana leaves treated with Exl1 protein to provide a genome-wide transcriptional framework associated with Exl1-triggered immunity. Comparative transcriptomic analysis of Arabidopsis thaliana Col-0 and JA-impaired mutant jar1-1 revealed distinct transcriptional patterns associated with JA-dependent responses at early time points. Abscisic acid (ABA)-related signaling was associated with later stages of the response, supported by the increased expression of the ABA-responsive gene CRK45 six hours after Exl1 treatment, and increased susceptibility of an ABA-impaired mutant. These findings suggest the involvement of multiple phytohormone-related pathways following Exl1 treatment. In parallel, extensive transcriptional reprogramming was observed, across diverse functional categories, reflecting a broad host response associated to the presence of Exl1. Together, these findings suggest that Exl1 induces an integrated signaling network that coordinates immune responses to strengthen plant defense, providing new insight for future functional studies on how bacterial expansins modulate plant-microbe interactions.